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Showing papers on "Gene published in 1969"


Journal ArticleDOI
25 Jul 1969-Science
TL;DR: Direct support for the idea that regulation of gene activity underlies cell differentiation comes from evidence that much of the genome in higher cell types is inactive and that different ribonucleic acids are synthesized in different cell types.
Abstract: Cell differentiation is based almost certainly on the regulation of gene activity, so that for each state of differentiation a certain set of genes is active in transcription and other genes are inactive. The establishment of this concept (1) has depended on evidence indicating that the cells of an organism generally contain identical genomes (2). Direct support for the idea that regulation of gene activity underlies cell differentiation comes from evidence that much of the genome in higher cell types is inactive (3) and that different ribonucleic acids (RNA) are synthesized in different cell types (4).

1,898 citations


Journal ArticleDOI
TL;DR: A technique is described for forming molecular hybrids between RNA in solution and the DNA of intact cytological preparations and a low level of gene amplification was also detected in premeiotic nuclei (oogonia) of the toad Xenopus.
Abstract: A technique is described for forming molecular hybrids between RNA in solution and the DNA of intact cytological preparations. Cells in a conventional tissue squash are immobilized under a thin layer of agar. Next they are treated with alkali to denature the DNA and then incubated with tritium-labeled RNA. The hybrids are detected by autoradiography. The technique is illustrated by the hybridization of ribosomal RNA to the amplified ribosomal genes in oocytes of the toad Xenopus. A low level of gene amplification was also detected in premeiotic nuclei (oogonia).

1,171 citations


Journal ArticleDOI
23 May 1969-Science
TL;DR: The presence of extrachromosomal nucleoli in amphibian oocytes has permitted isolation and electron microscopic observation of the genes coding for ribosomal RNA precursor molecules.
Abstract: The presence of extrachromosomal nucleoli in amphibian oocytes has permitted isolation and electron microscopic observation of the genes coding for ribosomal RNA precursor molecules. Visualization of these genes is possible because many precursor molecules are simultaneously synthesized on each gene. Individual genes are separated by stretches of DNA that apparently are not transcribed at the time of synthesis of precursor rRNA in the extrachromosomal nucleoli.

812 citations



Journal ArticleDOI
01 Nov 1969-Virology
TL;DR: It appears that in T7 (as in T4 and lambda) related functions tend to cluster along the genetic map, which makes this system a very attractive one in which to study a number of biological problems at the molecular level.

487 citations


Journal ArticleDOI
22 Aug 1969-Science

291 citations


Journal ArticleDOI
TL;DR: The rate of amino acid substitutions in the evolution of homologous proteins is remarkably constant as discussed by the authors, which is consistent with the hypothesis that a majority of the amino acid substitution that occurred in these proteins are the result of random fixation of selectively neutral or nearly neutral mutations.
Abstract: The rate of amino acid substitutions in the evolution of homologous proteins is remarkably constant. Furthermore, estimated rates of amino acid substitutions based on comparisons of the alpha hemoglobin chains of various mammals with that of the carp are about the same as those based on comparisons of the carp alpha and mammalian beta or the alpha and beta chains in mammals. These uniformities are regarded as evidence for the hypothesis that a majority of amino acid substitutions that occurred in these proteins are the result of random fixation of selectively neutral or nearly neutral mutations. Two implications of this possibility are discussed: (a) Random gene frequency drift is playing an important role in determining the genetic structure of biological populations and (b) genes in “living fossils” may be expected to have undergone as many DNA base (and therefore amino acid) substitutions as corresponding genes (proteins) in more rapidly evolving species.

284 citations


Journal ArticleDOI
TL;DR: An examination of messenger RNA relatively specific for the lactose operon suggests that specific chromosomal genes may diverge more or less than the genome as a whole and Ribosomal ribonucleic acid (RNA)-specific sequences are conserved among most enterobacteria.
Abstract: Polynucleotide relationships were examined among many representatives of the Enterobacteriaceae by means of agar, membrane filter, and hydroxyapatite procedures. The amount of deoxyribonucleic acid (DNA) that reassociated was dependent, especially in interspecific reactions, on the annealing temperature. In only three cases: Escherichia coli-Shigella flexneri, Salmonella typhimurium-S. typhi, and Proteus mirabilis-P. vulgaris, was relative interspecific duplex formation 80% or higher. In most cases interspecies DNA duplex formation was 40% or less of that obtained from intraspecies DNA reassociation reactions. The stability of E. coli-S. flexneri DNA duplexes formed at either 60 or 75 C was virtually identical to that of homologous E. coli DNA duplexes, and the degree of interspecies duplex formation was minimally affected by the temperature increase (86% at 60 C; 77% at 75 C). The thermal stability of DNA duplexes formed at 60 C between DNA from E. coli and DNA from strains of Aerobacter aerogenes, S. typhimurium, S. typhi, and P. mirabilis was about 12 to 14 C below that of reassociated E. coli DNA. At 75 C, the formation of the interspecific DNA duplexes was markedly decreased, but the stability of the DNA able to reassociate at this temperature approximated that of reassociated E. coli DNA. The degree of reassociation and the thermal stability of E. coli-S. flexneri DNA duplexes suggests relatively little evolutionary divergence in these organisms. The other enterobacteria tested, however, have diverged to a point where less than one-half of their DNA can reanneal with E. coli DNA at 60 C and less than 10% reacts at 75 C. The degree of divergence between various enterobacteria does not appear to be uniform along the DNA molecule. Ribosomal ribonucleic acid (RNA)-specific sequences are conserved among most enterobacteria. An examination of messenger RNA relatively specific for the lactose operon suggests that specific chromosomal genes may diverge more or less than the genome as a whole.

276 citations


Journal ArticleDOI
20 Dec 1969-Nature
TL;DR: The mutation affecting DNA polymerase activity in the mutant strain isolated by De Lucia and Cairns is located between metE and rha, at approximately 75 minutes on the Escherichia coli chromosome.
Abstract: The mutation affecting DNA polymerase activity in the mutant strain isolated by De Lucia and Cairns is located between metE and rha, at approximately 75 minutes on the Escherichia coli chromosome. The mutation is recessive to the wild-type gene in partial diploids. It is an amber nonsense mutation which responds to the suppressors Sul+, Sull+ and Sulll+. Strains carrying the mutation are not deficient in carrying out genetic recombination.

210 citations


Journal ArticleDOI
01 Nov 1969-Virology
TL;DR: The protein composition of purified T7 phage particles, the patterns of protein synthesis after infection with wild-type and amber mutants of T7, and molecular weights of the individual polypeptide chains have been examined by electrophoresis on polyacrylamide gels containing SDS at neutral pH.

176 citations



Journal ArticleDOI
01 Sep 1969-Virology
TL;DR: These results, together with results published elsewhere, show that gene 3 codes for the phage attachment protein, probably present as a single subunit at one end of the filamentous virion, while gene 8 code for the major coat protein subunit.

Book ChapterDOI
TL;DR: This chapter reveals the use of genetic modification to improve the protein quality of a plant and the most probable avenue to important changes in amino acid composition involves changing the relative proportions of metabolically inert storage proteins that have quite different amino acid compositions.
Abstract: Publisher Summary This chapter reveals the use of genetic modification to improve the protein quality of a plant. A realistic assessment of the prospects of increasing the protein quality of any crop plant depends on an understanding of the genetic control of protein structure. The information contained in a gene is a linear codescript consisting of a unique sequence of trinucleotide codons—DNA. The information is transcribed into a complementary sequence of trinucleotide codons of RNA (the messenger RNA) that is translated in turn into the amino acid sequence of a particular protein. The 20 amino acids that are the usual components of protein are coded by trinucleotide codons. As there are 4 nucleotide components of DNA, there are 64 (4 3 ) possible codons. Serious attention should be given to the identification and utilization of mutant genes that raise the concentration of the limiting amino acids in both cereals and legumes that are important sources of protein for humans and livestock. The improvement of the nutritional quality of traditional foods has many advantages, particularly in developing nations where it may be difficult to reach large segments of the population with nutritional supplements. From theoretical considerations involving the genetic control of protein synthesis, it is probable that the most probable avenue to important changes in amino acid composition involves changing the relative proportions of metabolically inert storage proteins that have quite different amino acid compositions. The supply of readily available plant protein may also be increased by the selection of strains lacking or low in toxic substances that must be destroyed or extracted before the seed proteins of cotton and many species of the Cruciferae can be utilized.

Journal ArticleDOI
TL;DR: A number of mutations expressed as cold-sensitive conditional lethal pheno-types were screened by transduction for their linkage to the streptomycin-resistance locus; 7 showed such linkage.
Abstract: A number of mutations (45) expressed as cold-sensitive conditional lethal pheno-types were screened by transduction for their linkage to the streptomycin-resistance locus; 7 showed such linkage. Of these, two were studied in greater detail. The sedimentation profiles of ribosomes from cultures grown at low temperature differed from wild type and from one another. Both mutants lost ribonucleic acid control at low temperature. It is suggested that a high proportion of mutants expressing a cold-sensitive phenotype harbor mutations in genes affecting ribosome synthesis or regulation.

Journal ArticleDOI
TL;DR: Phage proteins are synthesized at nearly normal rates in cells in which replication of phage double-stranded DNA is blocked by gene 2 mutations, suggesting that the initial double- Stranded DNA molecule serves as the principal template, perhaps the only template, for phage messenger RNA synthesis.
Abstract: Particles of the small filamentous coliphage M13 contain not only the major coat protein, which is the product of phage gene 8, but also a minor coat protein, the A protein, which is the product of gene 3. The A protein has a molecular weight of approximately 70,000 daltons, is present in one copy per virion, and is responsible for phage attachment to host cells. Also associated with purified M13 particles is a minor quantity of very small proteinaceous material, but its origin as a phage-coded product has not been demonstrated. At least five phage-specific proteins, including the two coat proteins, are present in appreciable quantities in M13-infected cells. The principal phage protein synthesized is the product of gene 5, which is responsible for phage single-stranded DNA synthesis. This protein has a molecular weight of about 8,000 daltons. Its precise function in DNA synthesis is not yet known. Phage proteins are synthesized at nearly normal rates in cells in which replication of phage double-stranded DNA is blocked by gene 2 mutations. This result suggests that the initial double-stranded DNA molecule serves as the principal template, perhaps the only template, for phage messenger RNA synthesis.

Journal ArticleDOI
01 Aug 1969-Virology
TL;DR: It appears that the l strand transcription of the b2 region does depend on coupling between b2 and the early N- a ′ genes; this link is characteristic of the DNA extracted from phage particles and of the circularized genomes, but is disrupted in the singly lysogenic form of λ, which is cyclicly permuted.

Journal ArticleDOI
06 Sep 1969-Nature
TL;DR: It is reported that streptolydigin inhibits chain elongation by E. coli RNA polymerase as was found by Siddhikol et al.4 and that, as is the case of rifampicin resistance1,2, the “core” enzyme (the α2ββ′ structure which itself possesses enzymatic activity) is modified in the resistant mutant.
Abstract: THE RNA polymerase of Escherichia coli consists of two small subunits α, two larger subunits β and β′, and one subunit σ which aids initiation1. A question relevant to control of polymerase synthesis is whether genes coding for the various subunits are contiguous. Both rifampicin resistant RNA polymerase and streptovaricin resistant RNA polymerase map near the argH locus2,3. Here I report that (a) streptolydigin inhibits chain elongation by E. coli RNA polymerase as was found by Siddhikol et al.4 for the polymerase of B. megaterium, (b) mutants altering the polymerase to streptolydigin resistance also map near argH, and (c) that, as is the case of rifampicin resistance1,2, the “core” enzyme (the α2ββ′ structure which itself possesses enzymatic activity) is modified in the resistant mutant.

Journal ArticleDOI
01 Dec 1969-Genetics
TL;DR: The results indicate that genome simplicity extends to other Drosophila species and to a representative of another Dipteran family, and there are variations among Diptera in genome size as inferred from the informational content of nucleotide sequences.
Abstract: A remarkable feature of evolution in the genus Drosophila is the conservation of the basic karyotype. Postulation of Robertsonian centric fusions (ROBERTSON 1916) is sufficient to explain most of the karyotypic rearrangements found in the various species. The fixation of large duplications of genetic material during the evolution of this genus appears to have been rare (STONE 1955). On the other hand, amino acid sequence data for proteins of other organisms indicate that many cistrons have very similar nucleotide sequences, and are presumably related by prior gene duplication (JUKES 1966). Physical studies of DNA of various eucaryotes also suggest that these genomes contain very large families of related cistrons (BRITTEN and KOHNE 1968). The size of such families is often in excess of that inferred from existing protein data (BRITTEN and KOHNE 1968; MCCARTHY 1967; WETMUR and DAVIDSON 1968). This may in some cases reflect the presence of cistrons with similar nucleotide sequences which specify proteins of overtly different functions. It is also likely that some of these families of genes have functions other than the determination of amino acid sequences. In keeping with the cytological studies, the reassociation kinetics of denatured Drosophila melanogaster DNA imply that the genome of this organism is much less complex, in terms of intragenome nucleotide sequence homologies, than those of vertebrates (LAIRD and MCCARTHY 1968b). Estimates made from these measurements suggest that perhaps 90% of D. melanogaster nucleotide sequences are not closely related to others elsewhere in the genome. In light of the extensive diversity within the genus Drosophila (LAIRD and MCCARTHY 1968a) , a detailed analysis of the intragenome homologies of representative species is expected to provide information about the evolution of genomes. In particular, our results indicate that genome simplicity extends to other Drosophila species and to a representative of another Dipteran family. In addition, there are variations among Diptera in genome size as inferred from the informational content of nucleotide sequences. MATERIALS AND METHODS Details of labeling and isolation of DNA and RNA from Drosophila, preparation of filterbound DNA, hybridization and duplex formation procedures, and analytical CsCl pycnography

Journal ArticleDOI
TL;DR: The development of a virus is programmed by a series of negative and positive controls which determine the timing and the segment on either of the two DNA strands to be transcribed into specific messenger RNA's.
Abstract: The development of a virus is programmed by a series of negative and positive controls which determine the timing and the segment on either of the two DNA strands (l or r) to be transcribed into specific messenger RNA's. Bacteriophage λ provides one of the most deeply studied systems for following the development of lysogenic viruses. In the lysogenic repressed state, only 2–4% of the λ genome is expressed. This pc-cI-rex region is transcribed leftward to produce a repressor protein which prevents any further transcription by blocking the oL and oR operators flanking the cI-rex operon (figs. 1, 2). This negative control is relieved by destruction of the repressor, and the result is the “induction” of viral development. The earliest post-induction or postinfection events are the leftward transcription of the pLoL N region from strand l and the rightward transcription mainly of the pRoR-x segment from strand r. The N product acts as a positive control, permitting a leftward transcription beyond gene N and a rightward transcription of genes cII-O-P and also Q. The int-xis system controls the excision of the λ genome, whereas the act of rightward transcription and the products of genes O and P initiate the replication of λ DNA. The product of gene Q, still another positive control, stimulates rightward transcription of the late genes which control the synthesis and assembly of the phage heads and tails as well as cell lysis. Among other types of negative control are the possible competition between the two divergent transcriptions originating in region x, the “antirepressor” effect of the x product, and the interference between the two convergent transcriptions which collide in the central b2 region. The majority of controls are based on protein-DNA interactions and can be modified by mutations. For instance, transcription can be rendered independent of negative repressor control either by constitutive, v, mutations which decrease or abolish the affinity of the o operators for the repressor or by insertion of new promoters–e.g., c17 or ric- on the “downstream” side of the operator. The need for the positive N and Q controls may also be obviated by mutations in the N- or Q-dependent promoter or terminator elements. The specific DNA structure within the controlling sites is not known. However, a remarkable coincidence was observed; namely, the occurrence of pyrimidine-rich clusters in those segments of the individual DNA strands acting as templates for RNA synthesis. This observation, which pertains to all studied DNA's, including those of phages T2, T3, T4, T5, T6, T7, λ, and ϕ 80, formed the basis for a proposal that implicates pyrimidine-rich clusters in the initiation, control and/or termination of transcription, and also in the determination of the preferred strand and, consequently, the orientation of transcription. General considerations regarding the possible role of the structural singularities, especially those represented by the pyrimidine clusters, in the bipartite structure of the recognition regions in DNA are discussed.

Journal ArticleDOI
01 Dec 1969-Virology
TL;DR: The results are taken to indicate that the virus initiates chromosomal DNA synthesis but that infection eventually results in extensive destruction of the cell genome, and thus the death of the cells.

Journal ArticleDOI
TL;DR: The hypothesis that histones, the bas ic proteins of the cell nuclei, inhibit gene activity in the cell is developed, and one can assume histones to be involved in the organization of chromosomes and in prolonged switching off of genes.
Abstract: It is now well established that the entire genetic information is con­ served in DNA base s equence. Each cell of the multicellular organism con­ tains the same DNA. In other words, each cell possesses the same genetic information. However, due to the pronounced differences in their protein composition, these cells are quite different in their properties. Thus only part of the genetic information is realized in each cell. The realization of genetic information, or gene expression, consists of a number of steps. The more important steps are: transcription or RNA synthesis, transport of RNA to the sites of protein synthesis, and translation or protein synthesis in ribosomes on the messenger RNA template. At any step of this complex process, some limitation of information may occur and the "information stream" may narrow. As a result, only part of the DNA base sequence is realized in polypeptide chains. The first step of such a limitation process is transcription. A number of papers have appeared to indicate that RNA in different tissues of the same organism is synthesized on different parts of the genome. This has been demonstrated with the aid of the competitive-hy­ bridization technique between DNA and RNA's isolated from different tis­ sues of the same species (1). Thus the question of the mechanism of this limitation of transcription arises. What are the molecular mechanisms of this "switching off" of some DNA molecules from the biosynthesis of messenger RNA (or their "mask­ ing") ? In 1945 the English scientists Stedman & Stedman (2) developed the hypothesis that histones, the bas ic proteins of the cell nuclei, inhibit gene activity in the cell. It should be pointed out that the appearance of histones in evolution takes place at the same time that organisms acquire two other fundamental properties . One of these properties is the separation of the nu­ cleus from the cytoplasm by a membrane. This distinguishes two main groups of organisms : prokaryotes and eukaryotes. Prokaryotes do not con­ tain histones in the nuclei [see for an example (3)]. The second fundamental property, which is especially pronounced in multicellular organisms, is differentiation. Thus the appearance of histones in evolution roughly coincides with the appearance o f a well-defined nucleus (and chromosomes ) and with differentiation. Therefore, one can assume histones to be involved in the organization of chromosomes and in prolonged switching off of genes. This long-term masking of some of the genes may

Journal ArticleDOI
TL;DR: Adding cyclic adenosine 3'5'-monophosphate to the cell-free system improved the yield of beta-galactosidase enzymatic activity by 8 to 30 times and the efficiency of repression from 50 to 95 per cent.
Abstract: A cell-free system allowing for synthesis of β-galactosidase enzymatic activity has been developed. This system requires DNA containing the β-galactosidase gene, a cell-free extract of Escherichia coli bacteria, and the low-molecular-weight components necessary for transcription of the DNA and translation of the resulting messenger RNA. Such a system is useful for studying enzyme synthesis, as well as its regulation. The gene for β-galactosidase is part of the lac operon whose expression is under the control of the lac repressor. In whole cells the lac repressor inhibits almost all of the gene expression for β-galactosidase. In the cell-free system, we had previously been able to repress about half the gene expression. Adding cyclic adenosine 3′5′-monophosphate to the cell-free system improved the yield of β-galactosidase enzymatic activity by 8 to 30 times and the efficiency of repression from 50 to 95 per cent.


Journal ArticleDOI
TL;DR: In vitro protein synthesis directed by bacteriophage MS2 RNA is inhibited by prior incubation of the RNA with MS2 coat protein, and coat protein inhibition results from the binding of a small number of protein molecules to the phage RNA at one or more sites outside the coat protein gene and prevents the translation of the other phage genes.

Journal ArticleDOI
20 Sep 1969-Nature
TL;DR: After release of repression, λ DNA quickly becomes associated with a membrane fraction that requires the product of the λ regulator gene N, but not the products of any known genes subject to N activation.
Abstract: After release of repression, λ DNA quickly becomes associated with a membrane fraction. This membrane association requires the product of the λ regulator gene N, but not the product of any known genes subject to N activation. Gene N may carry out its positive regulation of DNA replication and RNA transcription through direct control of membrane association.

Journal ArticleDOI
TL;DR: On the basis of genetic analyses, it appears that the remainder of the genetic material of the trp operon of the E R strain is unaltered, since the regions responsible for normal operator, promoter and the other structural genes of the operon can be separated from the ER strain.

Journal ArticleDOI
TL;DR: Many of the genes involved in motility and chemotaxis in Escherichia coli are homologous to those which have been studied in Salmonella typhimurium.
Abstract: In Escherichia coli, the following genes are involved in motility and chemotaxis. The H gene is the structural gene for flagellin. Mutation in the mot gene results in paralysis of the flagella, and mutation in the fla genes leads to an absence of flagella. The cheA, cheB, and cheC genes are required for chemotaxis. The chromosomal location of these genes has now been determined. The majority are clustered in a small region around uvrC, between his and aroD, in the order his-cheC-H-uvrC-mot-cheA-cheB-aroD. The fla genes are located in the same region, and also between trp and gal. The results indicate that many of the genes are homologous to those which have been studied in Salmonella typhimurium.

Journal ArticleDOI
TL;DR: The isolation of additional amber mutants in two genes of the FST-DNA (genes I and II), and of temperature-sensitive mutants in gene I are described, confirming genetically and biochemically the specificity and two of its functions in the viral growth cycle.

Journal ArticleDOI
TL;DR: The existence of a large number of starter sequences for DNA-dependent RNA polymerase on the phage genome is suggested, suggesting a simultaneous reading of the rII region by several polymerase molecules.

Journal ArticleDOI
TL;DR: It is shown that in Chinese hamster cells rRNA cistrons duplicate like the bulk of DNA, once in a cell cycle.
Abstract: Because of the redundancy of ribosomal RNA cistrons and in analogy with a few known special cases, one may postulate that a few “master genes” for rRNA direct the synthesis of multiple copies of themselves per cell cycle. We have shown that in Chinese hamster cells rRNA cistrons duplicate like the bulk of DNA, once in a cell cycle. The time during the S-phase at which rRNA genes duplicate has also been determined by means of RNA-DNA hybridization studies. The time of duplication of rRNA genes occurs between t= 1.5 and t= 3.0 hours from the beginning of the S-phase.