Showing papers in "The Japanese Journal of Genetics in 1991"

The neutral theory of molecular evolution: a review of recent evidence.

Abstract: In sharp contrast to the Darwinian theory of evolution by natural selection, the neutral theory claims that the overwhelming majority of evolutionary changes at the molecular level are caused by random fixation (due to random sampling drift in finite populations) of selectively neutral (i.e., selectively equivalent) mutants under continued inputs of mutations. The theory also asserts that most of the genetic variability within species at the molecular level (such as protein and DNA polymorphism) are selectively neutral or very nearly neutral and that they are maintained in the species by the balance between mutational input and random extinction. The neutral theory is based on simple assumptions, enabling us to develop mathematical theories based on population genetics to treat molecular evolution and variation in quantitative terms. The theory can be tested against actual observations. Neo-Darwinians continue to criticize the neutral theory, but evidence for it has accumulated over the last two decades. The recent outpouring of DNA sequence data has greatly strengthened the theory. In this paper, I review some recent observations that strongly support the neutral theory. They include such topics as pseudoglobin genes of the mouse, αA-crystallin genes of the blind mole rat, genes of influenza A virus and nuclear vs. mitochondrial genes of fruit flies. I also discuss such topics as the evolution of deviant coding systems in Mycoplasma, the origin of life and the unified understanding of molecular and phenotypic evolution. I conclude that since the origin of life on Earth, neutral evolutionary changes have predominated over Darwinian evolutionary changes, at least in number.

Restriction fragment length polymorphism (RFLP) analysis in wheat. II. Linkage maps of the RFLP sites in common wheat

Abstract: Sixty-six F2 plants from the cross, Triticum aestivum cv. Chinese Spring (abbrev. CS) x T. spelta var. duhamelianum (Spelta), exhibiting the greatest number of RFLPs among eight common wheats, were analyzed for their RFLP genotypes using genomic DNA clones of CS as probes. In total, 204 RFLP loci were identified and their linkage relationships established. By nulli-tetrasomic analyses, all linkage groups were assigned to one another of the 21 wheat chromosomes. In addition, the carrier chromosomes of 228 non-RFLP loci were identified. The linkage maps of these RFLP loci have a total size of 1800 cM and exceed those of the classical genes in both size and locus number. Twenty loci show distorted segregation, four of which are clustered on chromosome 4A and three on the 2D chromosome. The CS alleles on 4A exhibit preferential transmission, while those on 2D exhibit depressed transmission, compared with Spelta alleles. This suggests the influence of gametic factors in those regions. RFLP loci are much fewer in the D genome than in the A and B genomes, but the numbers of non-RFLP loci are nearly the same in these three genomes. This suggests that Spelta wheat originated from a hybridization between T. dicoccum (spelt emmer) and T. aestivum.

Mutability of constitutive heterochromatin (C-bands) during eukaryotic chromosomal evolution and their cytological meaning

Abstract: A quantitative analysis of the alterations of constitutive heterochromatin in eukaryotic chromosomal evolution was attempted using the accumulated C-banding data available for mammals, amphibians, fish, ants, grasshoppers, and plants. It was found that these eukaryotes could be classified into two types by their C-banding patterns: 1) Type I included mammals, fish, and ants, and 2) Type II included amphibians, grasshoppers, and plants. C-bands were rather scarce in Type I eukaryote chromosomes and were found around the pericentromeric region when present at all, whereas the predominance of interstitial or terminal C-bands was found in Type II eukaryote chromosomes. The Type I and II C-banding patterns can best be interpreted by assuming that in the former group of eukaryotes the saltatory increase in constitutive heterochromatin occurs preferentially at the pericentromeric regions of telocentric chromosomes induced by centric fission, with C-bands being eliminated almost completely by centric fusion and/or pericentric inversion. On the other hand, C-bands appear in the Type II eukaryotes both interstitially and in the telomeric regions of chromosomes, and there may be no effective mechanism to eliminate these bands once they are integrated.

Diversification of the rice Waxy gene by insertion of mobile DNA elements into introns.

Abstract: The waxy (wx) gene of Oryza glaberrima was cloned, and its nucleotide sequence was determined. A waxy mutant of O. glaberrima showing a glutinous phenotype was found to contain a substitution mutation generating a termination codon in the coding region of the wx gene. The Wx sequence of O. glaberrima was different from that of Oryza sativa by substitutions and insertions/deletions, among which only a few substitutions occurred in several exons not to severely alter the amino acid sequence of the Wx protein. The most striking difference observed in introns was a 139-bp deletion (or insertion) in intron 10 of O. glaberrima (or O. sativa). In O. sativa, 125 bp of the 139-bp sequence was flanked by direct repeats of a 14-bp sequence. A sequence homologous to the 125-bp sequence was found in the region preceding exon 2; this sequence was also flanked by direct repeats of another 14-bp sequence. This result and the observation that the 125-bp sequence was interspersed in rice genomes indicate that they are SINEs (short interspersed elements) in the plant system. We also identified a DNA sequence with long terminal inverted repeats in intron 13 of both O. glaberrima and O. sativa. This sequence was present in multiple copies in rice genomes, suggesting that it is a transposable element. These results obtained suggest that mobile DNA elements have diversified the rice Waxy gene by inserting into introns, each of which may originally have a length of about 100 bp.

Genomic DNA sequences of two new genes for new storage protein glutelin in rice

Abstract: A new cDNA and two genomic genes encoding the rice storage protein glutelin were isolated and sequenced. The nucleotide sequence of one gene (GluA-3) was completely identical with that of the new cDNA identified here, and the other (GluA-4) was a pseudogene. These glutelin genes were closely related to each other, and belonged to the subfamily A containing the type I (GluA-1) and II (GluA-2) glutelin genes. The Northern blot analysis, using synthetic oligonucleotide specific to the GluA-3 gene as a probe, showed that this gene was expressed earlier than other glutelin genes during seed maturation.

Organization of DNA sequences highly repeated in tandem in rice genomes.

Abstract: Digestion of the total genomic DNA from rice Oryza sativa L. cv. C5924 with EcoRI generated an intense band of a DNA fragment of about 0.36 kb long. The DNA fragment cloned into pUC19 was used to hybridize with the total rice genomic DNA partially digested with EcoRI. A ladder of bands of DNA fragments with multiplied length of 0.36 kb was observed, demonstrating that this sequence occurs in tandem in the genome. The copy number of the sequence estimated by dot blot hybridization analysis was 2000-3000 copies per haploid genome from callus or seedling of C5924. This sequence was present in other O. sativa cultivars, such as Sasanishiki in 700-900 copies, Koshihikari in 3400-4300, and Nipponbare in 4600-6000 copies. Another rice species, O. glaberrima, also had this sequence in 540-680 copies, but four lines of foxtail millet had none. The DNA fragments containing the repeated sequences in Nipponbare were then cloned into lambda EMBL3, and sequences of nine units consecutively repeated and an AT-rich sequence connected with them in a phage clone could be determined. Each repeating unit showed sequence divergency mostly by substitution of bases in a range from 3% to 7%, when compared with a 355-bp consensus sequence. Analyses of the substituted bases indicate that these are due to spontaneous mutations which occurred at random, after reiteration of a unit sequence by unequal crossing over events. Gene conversion within the repeated sequences might have further diversified their sequences.

Variation of S-alleles and S-glycoproteins in a naturalized population of self-incompatible Brassica campestris L.

Abstract: Variation of S-alleles and S-glycoproteins associated with self-incompatibility was studied in a naturalized population of Brassica campestris growing in Oguni-machi, Japan. Of 58 plants collected from the population, 45 were self-incompatible and 8 were self-compatible. Of 32 families investigated on their selfed progenies, 30 families showed segregation fitting to one locus S-allele model of sporophytic self-incompatibility. From cross-pollination experiments between 35 S-homozygotes so far isolated, 16 different S-alleles were identified, and the number of S-alleles involved in this population was estimated to be 20-30. S-glycoproteins corresponding to each S-allele were determined by immunoblotting with polyclonal antibody against S8-glycoprotein. Concanavalin A and Coomassie Blue stainings were also applied to determining corresponding S-glycoproteins, but were not so clear as the antibody cross reaction. It is pointed out that a stigma involves a number of proteins with different pI points, which are cross-reactive with anti-S-glycoprotein-antiserum. Many of these proteins are heritable in correlation with major S-glycoproteins. Since the content of these proteins was variable, we tentatively classified major and minor S-glycoproteins, and assumed that these S-glycoproteins were controlled by S-like DNA sequences with closely linked S-locus. Beside these S-glycoproteins, presence of heterozygote specific proteins was also pointed out, suggesting occurrence of post-transcriptional modification of these proteins. The pI values of major S-glycoproteins ranged from 5.0-9.0 and those at 7.0-9.0 were frequent.

Isolation and Characterization of the adenylate cyclase structural gene of Neurospora crassa

Abstract: A single gene (nac) encoding an adenylate cyclase was cloned from the genomic DNA library of Neurospora crassa, using the DNA fragment encoding the catalytic domain of adenylate cyclase of Saccharomyces cerevisiae as a probe. The open reading frame of this gene (6900 base pairs) was interrupted three time by introns. The protein encoded consists of 2300 amino acids and has adenylate cyclase activity. N. crassa adenylate cyclase has a high degree of homology with the catalytic domains of yeast and bovine brain adenylate cyclases.

Diallel analysis of callus growth and plant regeneration in rice seed-callus

Abstract: Genetic characteristics of callus growth and plant regeneration in rice with seed-derived calli were studied in 6 × 6 diallel crosses using Japonica cultivars. Genetic parameters estimated by Hayman's method showed the high additive gene effects and involvement of two groups of genes for callus growth, which were identified as incomplete dominance. On the other hand, both dominance and additive effects were important for plant regeneration, and further epistatic effects were observed in this character, while the analysis of 5 × 5 subdiallel for plant regeneration showed non-epistatic relation and involvement of 2 groups of genes. Graphical analysis using Vr and Wr for the callus growth showed that Norin 1, Somewake and Daikoku 1 possessed dominant genes which suppress callus growth, while Kuju, Sasanishiki and Murasaki-ine whose callus growth was more vigorous had recessive genes. The frequency distribution of callus growth in F2 generation between Kuju and Somewake showed a segregation which agreed with the expected ratio for a single factor control (3:1). On the other hand, relationship between Vr and Wr in the 5 × 5 subdiallel for plant regeneration showed that Daikoku 1, which had a relatively high capacity for plant regeneration, possessed more dominant genes, while Norin 1 and Kuju, which had lower capacities, possessed recessive genes. The reciprocal F1s between Norin 1 and Somewake showed excellent capacities for plant regeneration (average of reciprocal crosses: 62%). Strategies for genetical improvement of plant regeneration are discussed.

Physical mapping of a male-fertility gene of common wheat.

Abstract: A terminal deletion in the short arm of chromosome 4B was obtained in the progeny of an alien monosomic addition line of common wheat (Triticum aestivum (L.) emend. Thell) with a chromosome from Aegilops cylindrica Host. Common wheat plants homozygous for the deletion were completely male sterile. The breakpoint was at about 84% of the length of the short arm from the centromere. Therefore, the male-fertility gene was located in the distal 16% region of the chromosome 4B short arm. This terminal deletion practically suppressed meiotic pairing between the short arms of the normal 4B and the deletion 4B chromosomes.

Phylogenetic relationships in the stone fruit group of Prunus as revealed by restriction fragment analysis of chloroplast DNA

Abstract: In order to clarify the genetic relationships among stone fruits, a restriction fragment analysis of chloroplast DNAs (cpDNAs) was applied to cultivated Prunus species, whose genetic diagnoses are difficult because of their heterogeneity and long life span. Chloroplast DNAs (cpDNAs) were extracted from leaves of nine stone fruit accessions covering six species of Prunus. A restriction fragment analysis was conducted by gel electrophoresis after digestion with these endonucleases. The genome sizes of the cpDNAs were about 135-139 kbp, and the fruits were classified into seven chloroplast genome types according to their restriction fragment patterns. Two peach cultivars and nectarine were found to harbor identical plastomes, differing from those of two wild peaches and the European plum. This suggests that two cultivated peaches (P. persica) did not receive the cytoplasm from the wild peaches, P. mira and P. davidiana. Phylogenetic relationships among these types were then estimated based on the shared common fragments among the species.

Molecular cloning and nucleotide sequencing of the Arthrobacter dextranase gene and its expression in Escherichia coli and Streptococcus sanguis.

Abstract: A bacterial strain, which assimilated dextran and water-insoluble glucan produced by Streptococcus mutans, was isolated from soil. The bacterium produced and secreted potent dextranase activity, which was identified as Arthrobacter sp. and named CB-8. The dextranase was purified and some enzymatic properties were characterized. The enzyme efficiently decomposed the water-insoluble glucan as well as dextran. A gene library from the bacteria was constructed with Escherichia coli, using plasmid pUC19, and clones producing dextranase activity were selected. Based on the result of nucleotide sequencing analysis, it was deduced that the dextranase was synthesized in CB-8 cells as a polypeptide precursor consisting of 640 amino acid residues, including 49 N-terminal amino acid residues which could be regarded as a signal peptide. In the E. coli transformant, the dextranase activity was detected mostly in the periplasmic space. The gene for the dextranase was introduced into Streptococcus sanguis, using an E. coli-S. sanguis shuttle vector that contained the promoter sequence of a gene for glucosyltransferase derived from a strain of S. mutans. The active dextranase was also expressed and accumulated in S. sanguis cells.

Morphogenesis of floral organs in Arabidopsis : predominant carpel formation of the pin-formed mutant

Abstract: A young flower stalk of pin-formed (pin) mutant of Arabidopsis thaliana forms no floral organ and bares its growing apex. In the latter stages of growth the apex of the flower stalk becomes fasciate or circular, and then develops numerous deformed flowers from its flanks. The flattening of the apex and the variety of flower morphology are more remarkable in the plants carried over winter in a greenhouse than those grown in a growth chamber of controlled temperature and light. The flowers of the pin mutant are entirely sterile, and the developed floral organs (sepal, petal, stamen and pistil) show various degrees of abnormality in number and shape. Among floral organs carpels are most predominantly formed, and the carpels often develop into pistils with ovary, stigma, papillae and ovule-like particles. Various homeotic transformations such as sepal-to-carpel, petal-to-carpel and stamen-to-carpel occur. The preferential carpel formation strongly suggests an epistatic relation between carpel gene(s) and genes controlling other floral organs, i.e., expression of carpel gene(s) is indispensable for differentiation of the four floral organs. If the genes controlling the development of sepals, petals or stamens would not function, carpeloid organs would inevitably appear on their whorls. The hierarchical relationship among the genes controlling the floral organ development is discussed.

Somatic mutation frequencies in the stamen hairs of Tradescantia grown in soil samples from the Bikini Island.

Abstract: Somatic pink mutation frequencies in the stamen hairs of Tradescantia BNL 02 clone grown for 76 days in two soil samples taken from the Bikini Island (where a hydrogen bomb explosion test had been conducted in 1954) were investigated. A significantly high mutation frequency (2.58±0.17 pink mutant events per 103 hairs or 1.34±0.09 pink mutant events per 104 hair-cell divisions) was observed for the plant grown in one of the two Bikini soil samples, as compared to the control plants (1.70±0.14 or 0.88±0.07, respectively) grown in the field soil of Saitama University. The soil sample which caused the significant increase in mutation frequency contained 6,880±330 mBq/g 137Cs, 62.5±4.4 mBq/g 60Co, and some other nuclides; a 150 μR/hr exposure rate being measured on the surface of the soil sample. The effective cumulative external exposures measured for the inflorescences of the plant grown in this soil sample averaged at most 60.8 mR, being too small to explain the significant elevation in mutation frequency observed. On the other hand, internal exposure due to uptake of radioactive nuclides was estimated to be 125 mrad (1.25 mGy) as an accumulated effective dose, mainly based on a gamma-spectrometrical analysis. However, it seemed highly likely that this value of internal exposure was a considerable underestimate, and the internal exposure was considered to be more significant than the external exposure.

Selective transmission of mitochondrial DNA in heteroplasmic lines for intra- and interspecific combinations in Drosophila melanogaster

Abstract: The transmission of mitochondrial DNA (mtDNA) was investigated in the heteroplasmic lines of Drosophila melanogaster at 19 degrees C and at 25 degrees C. The selective transmission of one type of mtDNA was dependent on the temperature at which the lines were maintained. In heteroplasmic lines for an intraspecific combination induced by germ-plasm transplantation using D. melanogaster as a germ-plasm donor, the proportion of donor mtDNA decreased in four out of five lines examined, the decreasing rate of which being greater at 25 degrees C than at 19 degrees C. Donor mtDNA was lost by the 20th generation at 25 degrees C. For an interspecific combination using D. mauritiana as a germ-plasm donor, the proportion of donor mtDNA increased and endogenous mtDNA was replaced with donor mtDNA at 25 degrees C. But donor mtDNA was almost lost at 19 degrees C by the 14th generation in all four lines examined. Possible mechanisms involved in the temperature-dependent modes of mtDNA transmission are discussed.

Characterization of telomeres in Hordeum vulgare chromosomes by in situ hybridization. I, Normal diploid barley

Abstract: Telomeres are the physical ends of eukaryotic chromosomes. In order to characterize the telomeres of barley (Hordeum vulgare L.), in situ hybridization to somatic metaphase chromosomes was conducted, using the cloned telomere sequence from Arabidopsis thaliana. The results showed hybridization signals at both ends of all 14 chromosomes. No hybridization signals at interstitial sites were observed. These results indicate that the telomere sequences of Arabidopsis are also found on the ends of barley chromosomes. The hybridization signals were observed to vary in size between arms of the same chromosomes, indicating differences in copy numbers of the telomeric repeat. With in situ hybridization, the barley telomeres became physically visible under the light microscope.

On the robertsonian polymorphism found in the Japanese raccoon dog (Nyctereutes procyonoides viverrinus).

Abstract: Karyotypes of 39 Japanese raccoon dogs (NPV) which appeared in the literature and of 7 previously unreported specimens were examined. Thirty four individuals showed the standard karyotype 2K = 26M + 10A + (M)X + (A)Y + Bs (2n = 38 + Bs), where Bs are supernumerary chromosomes. The remaining 11 individuals had 2K = 25M + 12A + XY + Bs (2n = 39 + Bs) and one was 2K = 23M + 16A + XY + Bs (2n = 41 + Bs). The G- and C-banding analyses of both somatic and germ cells revealed that these karyotypes with odd numbers are heterozygous (M/A) for a single Robertsonian rearrangement of chromosomes 2, 5, 6, 8, or 11, and one is M/A heterozygous for three autosomes: 5, 6, and 11.

Comparison of somatic mutation frequencies in the stamen hairs of one mutable and two stable clones of Tradescantia treated with small doses of gamma rays

Abstract: Induced somatic pink mutation frequencies in the stamen hairs of Tradescantia KU 20 clone, a blue/pink heterozygote highly mutable spontaneously at lower temperature, were studied after treating with relatively small doses of 60Co gamma rays (39 to 551 mGy or 3.9 to 55.1 rad), and were compared with those of two stable clones (non-mutable spontaneously), BNL 02 and KU 9, which are also blue/pink heterozygotes. It was found that the gamma-ray-induced mutation frequency in KU 20 clone was comparable (18.8 pink mutant events per 104 hair-cell divisions per Gy) to those in BNL 02 (12.2 and 21.2) and KU 9 (17.4) clones, when the spontaneous mutation frequencies of KU 20 clone were relatively low (at most about 5.7 and 2.3 times of BNL 02 and KU 9 clones, respectively). However, when the spontaneous mutation frequencies of KU 20 clone were much higher (up to about 65 and 27 times of BNL 02 and KU 9 clones, respectively), induced mutation frequency was significantly higher in KU 20 clone (58.8 pink mutant events per 104 hair-cell divisions per Gy) than in BNL 02 and KU 9 clones. The extent of increase in the gamma-ray-induced mutation frequency in the latter case was nevertheless very much less than the increase in the spontaneous mutation frequency, suggesting different mechanisms of initiation and repair of radiation-induced and spontaneous mutations.

Physical map of chloroplast DNA of the onion Allium cepa L., showing the location of photosynthesis-related genes

Abstract: To compare the gene order of chloroplast genome among monocotyledonous plants, we constructed a physical map of chloroplast DNA (cpDNA) of onion (Allium cepa L. cv. Shounan red, 2n=16) with four restriction endonucleases, PstI, SalI, XhoI, and SmaI. The cpDNA of Allium cepa was found to be a circular molecule with a total size of ca. 155 kb and containing two inverted repeats of 26 kb each that disrupt the rest of the molecule into small (ca. 16 kb) and large (ca. 86 kb) single copy regions. The endonuclease recognition sites of the physical map were confirmed by Southern hybridizations of total onion cpDNA with homologous and heterologous probes. 16 genes were localized on the physical map of the onion cpDNA. Genome structure of onion cpDNA was similar in terms of genome size and gene order of cpDNA to that of tobacco cpDNA, differing from the cpDNA structure of gramineous plants.

A high efficient method for introduction of exogenous genes into Phycomyces blakesleeanus

Abstract: An efficient method is described for obtaining transformants in Phycomyces by microinjection of plasmid DNA carrying the kanamycin resistance gene from Tn903 into a young sporangium. Approximately 9% of the colonies, germinated from the spores which were developed in the sporangium, were resistant to G418 when a 36 ng sample of the transforming plasmid DNA was injected into a sporangium. The transformation efficiency (transfomants/total colonies) was about 350 times higher than that (transfomants/total protoplasts) obtained with the ordinary protoplast method.

Cytoplasmic diversity in alloplasmic common wheats with cytoplasms of Triticum and Aegilops revealed by photosynthetic and respiratory characteristics

Abstract: Photosynthetic and respiratory characteristics were surveyed to evaluate cytoplasmic diversities in alloplasmic common wheats in which a nuclear genome of common wheat (Triticum aestivum L cv Chinese Spring (CS)) was combined with cytoplasms of Triticum and Aegilops species The photosynthetic capacity (PSC) was measured based on the 13CO2-assimilation rate by infrared absorption spectrophotometry A significant variation was found in PSC The alloplasmic line with a cytoplasm of T monococcum ssp boeoticum which is unique in causing severe growth depression and male sterility when combined with CS nuclei showed more than 30% higher PSC than the euplasmic CS A negative correlation was found between PSC and growth vigor of the euplasmic and alloplasmic lines Respiratory electron flows and the cytochrome c oxidase (COX) activity were measured polarographically by an oxygen electrode The cytochrome path activity, the COX activity and the alternative path capacity showed significant variations among the lines, irrespective of plant tissues studied The alloplasmic line with T monococcum cytoplasm showed chracteristic respiration in the alloplasmic line: It significantly increased the alternative path capacity and the COX activity in roots and leaves of 2-week-old plants Moreover, the COX activity in the roots was negatively correlated with growth vigor among the lines The results suggested that the aberrantly high COX activity might be related to the growth depression of the alloplasmic CS with T monococcum cytoplasm

Physical mapping and RFLP analysis of mtDNAs from the ascosporogenous yeasts: Saccharomyces exiguus, S. kluyveri and Hansenula wingei.

Abstract: Mitochondrial DNAs from the ascosporogenous yeasts S. exiguus, S. kluyveri and H. wingei were prepared by a new rapid method without CsCl isopycnic centrifugation. The mtDNA RFLPs were identified and clearly distinguished each species from the other. The physical maps were constructed by single and double digestion with nine restriction endonucleases. The location of rRNA genes was assigned to the maps by Southern hybridization with synthetic consensus probes. The genome sizes of these mtDNAs were estimated to be 45 kb for S. exiguus, 54kb for S. kluyveri and 27kb for H. wingei. The mtDNA RFLP analysis indicates a phylogenetic relationship among these yeasts. This indicates that S. cerevisiae is closer to H. wingei than S. kluyveri. However, the derived phylogenetic tree is completely consistent with that which was previously constructed on amino acid replacement in mating pheromones and electrophoretic karyotypes (Yoshida et al., 1989).

Variation of spontaneous somatic mutation frequency in the stamen hairs of a mutable clone of Tradescantia, KU 20

Abstract: Variation of spontaneous somatic pink mutation frequency was studied in the stamen hairs of Tradescantia KU 20 clone, a highly mutable blue/pink heterozygote. The spontaneous mutation frequency varied greatly from 4.03±1.21 to 120±7 and from 18.8±3.1 to 110±5 pink mutant events per 103 hairs when the plants were grown outdoors and in the greenhouse, respectively, being generally higher at lower temperature and also in the greenhouse than in outdoors. The spontaneous mutation frequency under controlled environmental conditions also varied from 3.06±0.37 to 40.8±3.1 pink mutant events per 103 hairs, showing a clearer negative correlation with temperature. It was found that the spontaneous mutation frequency under controlled environmental conditions increased when day/night temperature shifts were applied, especially with a 5°C shift than with 3°C shifts. The difference between the highest and the lowest mutation frequencies reached almost 40 times, and this clone was confirmed to be a temperature-sensitive mutable clone. A repair mechanism of DNA damages occurring spontaneously, which is more effective at higher temperature, thus presumably an enzymatic one, is very likely involved in the mutable nature of this clone.

A new haplotype of the β-globin gene complex, Hbbw1, in Chinese wild mouse

Abstract: A new pattern was observed in the electrophoretic survey of the hemoglobin beta chain (Hbb) in Chinese wild mice, Mus musculus. The electrophoretic mobility of the major component of the new Hbb was identical to that of Hbbs on cellulose acetate plate, although it was almost identical to that of Hbbd or Hbbp on acrylamide gel. This suggests that the major component of Chinese Hbb has a unique primary structure. A minor component of the new Hbb was completely different from that of the other three Hbb haplotypes well known. These results indicate that the Hbb-b1 and Hbb-b2 of the new Hbb haplotype, assigned Hbbw1, are unique genes in their molecular structure. So far, Hbbw1 has been observed in northwestern China.

Suppression of the cr-1 mutation in Neurospora crassa.

Abstract: We have cloned a DNA fragment, which hybridized with the adenylate cyclase gene (CYR1) of Saccharomyces cerevisiae, from genomic DNA libraries of Neurospora crassa The cr-1 mutation was able to be suppressed by introducing this DNA fragment on a cosmid vector, judging from recovery of the adenylate cyclase activity and the abnormal morphology

Sequence analysis of a mitochondrial DNA fragment isolated from cultured cells of carrot cytoplasmic male-sterile strain.

Abstract: 2.0kb Hind III fragment isolated from cytoplasmic male-sterile carrot mitochondria, designated PKT5, was hybridized to ORF13 which is the coding region of a unique polypeptide in maize CMS (Dewey et al., 1986). Sequence analysis indicated that PKT5 is consisted of 3 domains. Domain 1 was identical to the 5'-flanking region of atp6 in maize CMS-TURF2H3 sequence (Dewey et al., 1986). Domain 2 contained a novel ORF encoding 72 amino acids, which was extremely homologous to the amino-terminal 67 amino acids of the unique ORF13 in maize CMS. Domain 3 except an amino acid change (Ile87=ATT for Asn87=AAT), was identical to ORF25 polypeptide in maize CMS. Connective sequences of these 3 domains were also highly homologous to the maize CMS-TURF2H3 sequence. Out of 7 recombination points in maize CMS-TURF2H3 sequence, at least 4 points were conserved in PKT5 sequence.

The viable 3.5n trouts produced between diploid females and allotriploid males.

Abstract: Eyed embryos and fingerlings of trouts between diploid females and allotriploid males were obtained. There were two groups, namely, one group with the chromosome number of 79-83 (group I), and another with that of 110-112 (group II). Judging from numbers and constitutions of the chromosomes, it is presumed that the individuals in group I were 2.5n and those in group II were 3.5n. All fingerlings were 3.5n, and 2 fingerlings of them were still surviving as of September, 1990, about 7 months after the hatching.

Temperature-dependency of electron-transport activity in mitochondria with exogenous mitochondrial DNA in Drosophila.

Abstract: In mitochondrial DNA (mtDNA) heteroplasmy induced artificially in Drosophila melanogaster (Matsuura et al., 1989), foreign mtDNA derived from D. mauritiana was selectively transmitted at 25 degrees C but was lost at 19 degrees C (Niki et al., 1989; Matsuura et al., 1990, 1991). To investigate temperature-dependent factors in the selective transmission of mtDNA, the temperature-dependency of electron-transport activity of mitochondria from D. melanogaster in which endogenous mtDNA was completely replaced by the foreign mtDNA was compared with that of D. melanogaster and D. mauritiana. For NADH-oxidase activity, the optimum temperature of D. mauritiana mitochondria was 35 degrees C while for two types of mitochondria from D. melanogaster each possessing either endogenous or exogenous mtDNA, maximum activity was noted at 32 degrees C. This observation suggests that the temperature-dependency of mitochondrial electron-transport activity is mainly determined by a nuclear genome. NADH-cytochrome c reductase and cytochrome c oxidase activities were not significantly different among the three types of mitochondria. The temperature-dependency of mitochondrial function apparently is not involved in the temperature-dependent selective transmission of mtDNA in the heteroplasmic state.

Further study on selective transmission of mitochondrial DNA in heteroplasmic lines of Drosophila melanogaster.

Abstract: The temperature-dependent transmission of mitochondrial DNA (mtDNA) was investigated in heteroplasmic lines of Drosophila melanogaster established by germ-plasm transplantation. Using D. melanogaster, D. simulans and D. mauritiana as germ-plasm donors, five recipient-donor combinations of heteroplasmy, differing from those previously examined (Matsuura et al., 1991), were constructed. For intraspecific reciprocal combinations, donor mtDNA in one combination was retained at 25 degrees C but was almost lost by the tenth generation at 19 degrees C. In the reciprocal, the proportion of the same type of recipient mtDNA decreased more quickly at 19 degrees C than 25 degrees C. Decreasing rates at 19 degrees C in the reciprocals differed from each other. For interspecific combinations, two species were used as germ-plasm donors. Donor mtDNA derived from D. simulans was lost at both temperatures and the rate of decrease was greater at 19 degrees C than 25 degrees C. The proportion of donor mtDNA derived from D. mauritiana increased at a greater rate at 25 degrees C than 19 degrees C when using two different strains of D. melanogaster as recipients. These results suggest that both the nuclear and two types of mitochondrial genomes are involved in the selective transmission of mtDNA.

Survival mechanism of dried calli and regeneration of plants in rice

Abstract: A system for long-term dry preservation of calli of rice (Oryza sativa L.) and a protection mechanism regulating the survival of dried calli were investigated. The highest survival of dried calli and the highest regeneration rate of plantlets were observed in calli which had been pretreated with 10-5 M abscisic acid (ABA) in the presence of 90 g/l of sucrose and were regrown on an R-2 medium. We detected a corresponding accumulation of the transcript RNA of the rab 16A gene (a rice gene induced by ABA and water stress) in dried calli, mature seeds, and calli pretreated with 10-5 M ABA. The levels of this mRNA increased with the increase of the sucrose concentation, indicating that the accumulation of rab 16A mRNA is regulated by ABA at higher concentrations of sucrose and related to the survival of dried calli. Analysis of proteins by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) demonstrated similar protein patterns in fresh and dried calli. However, in the dried calli pretreated with 10-5 M ABA and 90 g/l of sucrose, different protein patterns were found compared to those in a callus dried without the pretreatment, indicating that some specific polypeptides might be synthesized in the pretreated dried callus.