Showing papers on "Mutant published in 1981"
TL;DR: Characterization of haploid double- sec -mutant strains, with regard to the structure of the accumulated invertase and the morphology of the exaggerated organelles, allows assessment of the order in which the gene products are required, the sequence of invert enzyme maturation steps and a pathway of secretory organelle pathways.
764 citations
TL;DR: It was found that transport of ferric enterochelin and ferrichrome was also constitutive in the fur mutant cells, and that ferric citrate uptake could be induced by only 10 μM citrate in the growth medium in contrast to wild-type cells in which at least 100 μMcitrate was necessary.
Abstract: The lac genes were inserted with phage Mu(Ap, lac) into the fhuA, fepA, cir and tonB genes which specify components of iron uptake systems. The expression of lac in all these operon fusions was controlled by the availability of iron to the cells, thereby facilitating a quick and simple measurement of the expression of the genes listed above. In an iron rich medium under anaerobic conditions all systems were strongly repressed. fhuA was depressed at higher iron concentration than was fepA or cir, and tonB was repressed only under anaerobic conditions and could be induced by iron limitation. Mutants constitutive for the expression of beta-galactosidase were selected in a fhuA-lac fusion strain. The outer membrane proteins Cir, FhuA, FecA, 76K and 83K were made constitutively in such mutant strains. Therefore, they were termed fur mutants. In these fur mutant strains, the synthesis of a 19K protein was reduced. Furthermore, it was found that transport of ferric enterochelin and ferrichrome was also constitutive in the fur mutant cells, and that ferric citrate uptake could be induced by only 10 microM citrate in the growth medium in contrast to wild-type cells in which at least 100 microM citrate was necessary. The fepA gene was concluded to be under an additional control, because it was not fully derepressed by the fur mutation.
545 citations
TL;DR: A temperature-sensitive conditional lethal mutant is isolated that accumulates the precursor of the maltose-binding protein in the cytoplasm, and also accumulates precursors of alkaline phosphatase, lambda receptor protein and the ompF gene gene product.
494 citations
TL;DR: Findings suggest that the SNF1 locus is involved in the regulation of gene expression by glucose repression, and suggests that SUC2 encodes a protein, probably a dimer or multimer.
Abstract: Utilization of sucrose as a source of carbon and energy in yeast (Saccharomyces) is controlled by the classical SUC genes, which confer the ability to produce the sucrose-degrading enzyme invertase (Mortimer and Hawthorne 1969). Mutants of S. cerevisiae strain S288C ( SUC2 + ) unable to grow anaerobically on sucrose, but still able to use glucose, were isolated. Two major complementation groups were identified: twenty-four recessive mutations at the SUC2 locus ( suc2 - ); and five recessive mutations defining a new locus, SNF1 (for sucrose n on f ermenting), essential for sucrose utilization. Two minor complementation groups, each comprising a single member with a leaky sucrose-nonfermenting phenotype, were also identified. The suc2 mutations isolated include four suppressible amber mutations and five mutations apparently exhibiting intragenic complementation; complementation analysis and mitotic mapping studies indicated that all of the suc2 mutations are alleles of a single gene. These results suggest that SUC2 encodes a protein, probably a dimer or multimer. No invertase activity was detected in suc2 mutants.—The SNF1 locus is not tightly linked to SUC2 . The snf1 mutations were found to be pleiotropic, preventing sucrose utilization by SUC2 + and SUC7 + strains, and also preventing utilization of galactose, maltose and several nonfermentable carbon sources. Although snf1 mutants thus display a petite phenotype, classic petite mutations do not interfere with utilization of sucrose, galactose or maltose. A common feature of all the carbon utilization systems affected by SNF1 is that all are regulated by glucose repression. The snf1 mutants were found to produce the constitutive nonglycosylated form of invertase, but failed to produce the glucose-repressible, glycosylated, secreted invertase. This failure cannot be attributed to a general defect in production of glycosylated and secreted proteins because synthesis of acid phosphatase, a glycosylated secreted protein not subject to glucose repression, was not affected by snf1 mutations. These findings suggest that the SNF1 locus is involved in the regulation of gene expression by glucose repression.
430 citations
TL;DR: Results suggest that ribosomes play an important role in the export of lambda receptor to the outer membrane.
362 citations
TL;DR: Observations indicate that the 72-base-pair repeated sequences form an essential element in the early viral transcriptional promoter and explain the inability of such a deleted genome to complement an early temperature-sensitive mutant of SV40, tsA, as well as the failure to replicate its DNA.
Abstract: On the late side of the simian virus 40 (SV40) DNA replication origin are several sets of tandem repeated sequences, the largest of which is 72 base pairs long. The role of these sequences was examined through construction of deletion mutants of SV40. A mutant from which one of the 72-base-pair repeated units was removed is viable upon transfection of monkey kidney cells with viral DNA. Extension of this deletion into the second repeated unit, however, leads to nonviability, as recognized by the absence of early transcription and of tumor antigen production. These observations indicate that the 72-base-pair repeated sequences form an essential element in the early viral transcriptional promoter and explain the inability of such a deleted genome to complement an early temperature-sensitive mutant of SV40, tsA, as well as the failure to replicate its DNA. In a parallel experiment it was found that the extended deletion mutant was also unable to complement a late temperature-sensitive mutant of SV40, tsB. This suggests that the extended mutant is also defective in DNA replication or late transcription (or both).
361 citations
TL;DR: Analysis of DNA from a spontaneous DBA/2J d revenant showed that these mice lack ecotropic-specific MuLV DNA sequences and suggested that the dilute mutation resulted from integration of an ecotropic provirus into the mouse genome.
Abstract: The single endogenous DBA/2J ectropic provirus segregated concordantly with the dilute (d) coat colour mutation on chromosome 9 in 53/53 DBA/2J-derived recombinant inbred mouse strains and all seven inbred and mutant strains tested that carry the d allele. Analysis of DNA from a spontaneous DBA/2J d revertant (d+2J) showed that these mice lack ecotropic-specific MuLV DNA sequences and suggested that the dilute mutation resulted from integration of an ecotropic provirus into the mouse genome.
357 citations
TL;DR: Alterations in the ATP-dependent protease in the lon- mutants can account for the defect in intracellular proteolysis and perhaps also for the other phenotypic effects of this pleiotropic gene.
Abstract: In Escherichia coli, degradation of abnormal proteins is an energy-requiring process; it is decreased in mutants in the lon (capR or deg) gene. We find that the protein encoded by the lon gene is an ATP-dependent protease and is identical to protease La, recently described in E. coli. Both proteins are serine proteases that hydrolyze casein and globin, but not insulin, in the presence of ATP and Mg2+. Both respond to ATP, less well to other nucleoside triphosphates, and not to nonhydrolyzable ATP analogs. The purified lon protein has an apparent Mr of 450,000 and appears to be composed of four identical subunits. Its size, chromatographic behavior, and sensitivity to various inhibitors and heat are indistinguishable from those of protease La. Moreover, in a strain that carries additional copies of the lon+ allele on a plasmid, the content of protease La, but not of other proteases, is 2- to 10-fold greater than in the lon+ parent strain. Strains carrying the nonsense mutations capR9 and capR- also contain this ATP-dependent proteolytic activity, but it is present in substantially lower amounts and is inactivated by phosphocellulose chromatography, unlike the wild-type enzyme. Degradation of abnormal proteins in these lon- strains, which is slower than in the wild type, still requires ATP. Alterations in the ATP-dependent protease in the lon- mutants can account for the defect in intracellular proteolysis and perhaps also for the other phenotypic effects of this pleiotropic gene.
339 citations
TL;DR: Ti plasmid mutants derived from Agrobacterium tumefaciens strain Ach5 that induce tumors of abnormal morphology have been analyzed and evidence is presented showing that IS60 is transferred into the plant cell DNA as part of the T-DNA.
330 citations
TL;DR: The report reviews and evaluates the current literature on chemically induced specific locus mutations in the V79 Chinese hamster lung cell line, and discusses the protocols for quantitative mutation studies including measurements of cytotoxicity, mutant expression times, mutant selection agents, cell densities during selection, and the stability and verification of mutant phenotypes.
Abstract: The report reviews and evaluates the current literature (about 125 primary publications) on chemically induced specific locus mutations in the V79 Chinese hamster lung cell line. The V79 cell is convenient to use for mutagenesis studies since it has a rapid growth rate, high plating efficiency, and a stable karyotype. Mutation can be easily measured at either the hypoxanthine-guanine phosphoribosyl transferase or the Na+/K+ ATPase locus, both of which have been well characterized. Other less-studied markers are also described. We discuss the protocols for quantitative mutation studies including measurements of cytotoxicity, mutant expression times, mutant selection agents, cell densities during selection, and the stability and verification of mutant phenotypes. Mutations in the V79 cells by chemicals that require activation can be tested after their metabolism by cell homogenates or by intact cells, and the results with each type of activation are compared. For purposes of analysis, we classified a compound as mutagenic if it induced a mutation frequency that is at least 3 times higher than the spontaneous mutant frequency reported for that specific experiment. By this criterion two-thirds of the chemicals analyzed were mutagenic--; 11% with and 55% without metabolic activation. Of the 191 chemicals examined; 119 were polycyclic aromatic hydrocarbons; 25 were nitro or nitroso compounds, 9 were alkyl halides; 7 were purine or pyrimidine derivatives and the remaining 31 were from other chemical classes. We also defined mutagenic potency as the concentration of a compound that increases the mutant frequency by 10 times the spontaneous frequency. Mutagenic potencies of the compounds examined varied over a range of 5 X 10(6). We have also found large interlaboratory variations in the mutagenic potencies. Such variation in potency could be reduced by normalizing the results to a standard mutagen such as N-methyl-N'-nitro-N-nitrosoguanidine. The role of the V79 assay in mutagenicity and carcinogenicity testing is discussed and recommendations are suggested for future investigation.
TL;DR: A temperature-sensitive mutant produced by transfection of cells with intact DNA and a specific DNA fragment mutagenized with low levels of hydroxylamine did not make viral DNA, although temperature sensitivity of the viral DNA polymerase could not be demonstrated.
Abstract: We report on the properties of a temperature-sensitive mutant produced by transfection of cells with intact DNA and a specific DNA fragment mutagenized with low levels of hydroxylamine The plating efficiency of the mutant at 39 degrees C relative to that at 335 degrees C was 5 X 10(-6) The pattern of polypeptides produced at the nonpermissive temperature was similar to that seen with wild-type virus in infected cells treated with inhibitory concentrations of phosphonoacetic acid in that alpha and beta polypeptides were produced, whereas most gamma polypeptides were either reduced or absent Consistently, the mutant did not make viral DNA, although temperature sensitivity of the viral DNA polymerase could not be demonstrated Marker rescue studies with herpes simplex virus type 2 (HSV-2) DNA mapped the mutant in the L component within map positions 0385 and 0402 in the prototype (P) arrangement of the HSV-1 genome Analysis of the recombinants permitted the mapping of the genes specifying infected cell polypeptides 36, 35, 37, 195, 11, 8, 2, 43, and 44, but only the infected cell polypeptide 8 of HSV-2 was consistently made by all recombinants containing demonstrable HSV-2 sequences Marker rescue studies with cloned HSV-1 DNA fragments mapped the temperature-sensitive lesion within less than 10(3) base pairs between 0383 and 0388 map units Translation of the RNA hybridizing to cloned HSV-1 DNA, encompassing the smallest region containing the mutation, revealed polypeptide 8 (128,000 molecular weight), which was previously identified as a beta polypeptide with high affinity for viral DNA, and a polypeptide (25,000 molecular weight) not previously identified in lysates of labeled cells
TL;DR: Based on the studies of the E. coli top mutants, it appears that the supX gene, which was originally studied in Salmonella typhimurium, is likely to be the structural gene for DNA topoisomerase I, which has a more rapid rate of induction and a higher level of catabolite-sensitive enzymes including tryptophanase and beta-galactosidase.
Abstract: Mutations in top, the structural gene for Escherichia coli DNA topoisomerase I, have been identified and mapped at 28 min on the chromosome, near cysB. Strains carrying deletions of the top gene are viable. The top mutations, however, do exert pleiotropic effects on transcription and transposition. Mutants lacking DNA topoisomerase I have a more rapid rate of induction and a higher level of catabolite-sensitive enzymes including tryptophanase and beta-galactosidase. This general activation of transcription by top mutations can be attributed to an increase in the negative superhelicity of the DNA in vivo when the topoisomerase activity is abolished. The frequency of transposition of Tn5, a transposon carrying kanamycin resistance, is decreased by a factor of 40 or more in top mutants. A direct or indirect role of the topoisomerase in transposition is discussed. The transposition frequency of Tn3, however, is not dependent on top. Based on the studies of the E. coli top mutants, it appears that the supX gene, which was originally studied in Salmonella typhimurium [Dubnau, E. & Margolin, P. (1972) Mol. Gen. Genet. 117, 91-112] is likely to be the structural gene for DNA topoisomerase I.
TL;DR: The CDC24 gene product seems to be involved in selection of the budding site, formation of the chitin ring at that site, the subsequent localization of new cell wall growth to the buddingsite and the growing bud, and the balance between tip growth and uniform growth of the bud that leads to the normal cell shape.
Abstract: Temperature-sensitive yeast mutants defective in gene CDC24 continued to grow (ie, increase in cell mass and cell volume) at restrictive temperature (36 degrees C) but were unable to form buds Staining with the fluorescent dye Calcofluor showed that the mutants were also unable to form normal bud scars (the discrete chitin rings formed in the cell wall at budding sites) at 36 degrees C; instead, large amounts of chitin were deposited randomly over the surfaces of the growing unbudded cells Labeling of cell-wall mannan with fluorescein isothiocyanate-conjugated concanavalin A suggested that mannan incorporation was also delocalized in mutant cells grown at 36 degrees C Although the mutants have well-defined execution points just before bud emergence, inactivation of the CDC24 gene product in budded cells led both to selective growth of mother cells rather than of buds and to delocalized chitin deposition, indicating that the CDC24 gene product functions in the normal localization of growth in budded as well as in unbudded cells Growth of the mutant strains at temperatures less than 36 degrees C revealed allele-specific differences in behavior Two strains produced buds of abnormal shape during growth at 33 degrees C Moreover, these same strains displayed abnormal localization of budding sites when growth at 24 degrees C (the normal permissive temperature for the mutants); in each case, the abnormal pattern of budding sites segregated with the temperature sensitivity in crosses Thus, the CDC24 gene product seems to be involved in selection of the budding site, formation of the chitin ring at that site, the subsequent localization of new cell wall growth to the budding site and the growing bud, and the balance between tip growth and uniform growth of the bud that leads to the normal cell shape
TL;DR: In this article, the authors extended the genetic analysis of four mutants carrying defective MATα alleles in order to determine how the mating type locus controls yeast cell types: a, a, and a α.
TL;DR: The ino1 locus is identified as the structural gene for the enzyme and it is shown that the Mr = 62,000 subunit is largely absent from crude extracts prepared from wild type yeast grown in the presence of repressing concentrations of inositol.
TL;DR: Biological and biochemical studies of tsJ12 and of a ts+ revertant of this mutant demonstrate that glycoprotein gB is essential for infectivity at the level of penetration and further define the physical map location of the gene for this glycop protein.
TL;DR: Four of the waxy mutants including B3, a controlling-element mutation, are similar to wild type in molecular weight as determined by electrophoresis in SDS acrylamide gels.
Abstract: Minimal limits for the structural gene at the waxy locus have been set by investigations of the protein product of the gene. An altered protein is produced by four of the waxy mutants including B3 , a controlling-element mutation. All are similar to wild type in molecular weight as determined by electrophoresis in SDS acrylamide gels. At least three of the five wx controlling-element mutations studied have been shown to lie within the limits of the structural gene.
TL;DR: The observation that each of six fertilization-defective (fer) mutants has a different and discreet set of morphological defects shows that the strict sequence of morphogenetic events that occurs during wild-type spermatogenesis cannot arise because each event is dependent on previous events.
Abstract: Taking advantage of conditions that allow spermatogenesis in vitro, the timing and sequence of morphological changes leading from the primary spermatocyte to the spermatozoon is described by light and electron microscopy. Together with previous studies, this allows a detailed description of the nuclear, cytoplasmic, and membrane changes occurring during spermatozoan morphogenesis. By comparison with wild type, abnormalities in spermatogenesis leading to aberrant infertile spermatozoa are found in six fertilization-defective (fer) mutants. In fer-1 mutant males, spermatids appear normal, but during spermiogenesis membranous organelles (MO) fail to fuse with the sperm plasma membrane and a short, though motile. pseudopod is formed. In fer-2, fer-3, and fer-4 mutants, spermatids accumulate 48-nm tubules around their nuclei where the centriole and an RNA containing perinuclear halo would normally be. In all three mutants, spermatids still activate to spermatozoa with normal fusion of their MOs, but the pseudopods formed are aberrant in most fer-2 and fer-4 spermatozoa and in some fer-3 spermatozoa. In fer-5 mutant males, spermatozoa do not form. Instead, defective spermatids with crystalline inclusions and abnormal internal laminar membranes accumulate. In fer-6 mutant males, only a few spermatozoa form and these have defective pseudopods. These spermatozoa retain their fibrous bodies, a structure which normally disassembles in the spermatid. The time of appearance of developmental abnormalities in all of these mutants correlates with the temperature-sensitive periods for development of infertility. The observation that each of these mutants has a different and discreet set of morphological defects, a structure which normally disassembles in the spermatid. The time of appearance of developmental abnormalities in all of these mutants correlates with the temperature-sensitive periods for development of infertility. The observation that each of these mutants has a different and discreet set of morphological defects, a structure which normally disassembles in the spermatid. The time of appearance of developmental abnormalities in all of these mutants correlates with the temperature-sensitive periods for development of infertility. The observation that each of these mutants has a different and discreet set of morphological defects shows that the strict sequence of morphogenetic events that occurs during wild-type spermatogenesis cannot arise because each event is dependent on previous events. Instead, spermatozoa, like bacteriophages, must be formed by multiple independent pathways of morphogenesis.
TL;DR: The isolation of a resistant mutant which induces a TK of altered substrate specificity is described and it is shown that this virus retains pathogenicity for mice with only a slight attenuation of neurovirulence.
Abstract: Acyclovir (9-[2-hydroxyethoxymethyl]guanine or ACV) is a nucleoside analogue with considerable potential for the treatment of herpes simplex virus (HSV) infections in man1,2. Two virus-coded enzymes are important in the mechanism of action of this drug: thymidine kinase (TK) which initiates its activation by converting it to the monophosphate3 and DNA polymerase whose action is inhibited by ACV triphosphate4. Changes in either gene may confer resistance5–7, but all reported mutations in the TK gene have resulted in failure of the resistant virus to induce appreciable levels of the enzyme. Such TK− mutants arise readily in tissue culture systems8,9 where the enzyme is non-essential for virus replication10, but in animals they show considerably reduced pathogenicity and neurovirulence7,11–14. We now describe the isolation of a resistant mutant which induces a TK of altered substrate specificity and we show that this virus retains pathogenicity for mice with only a slight attenuation of neurovirulence.
TL;DR: These results identify for the first time native proteins whose stability is affected by the Lon proteolytic pathway and indicate that the Lon system may be important in regulating gene expression in E. coli.
TL;DR: Another region of the SV40 genome showed preferential binding to D2T, however, the decay rate of this site in the EcoRII/D fragment was rapid and, under these conditions, could not be distinguished from non-specific binding.
TL;DR: Methods have been developed for rapid isolation and genetic analysis of vaccinia virus mutants and four phenotypes appear: normal, a phenotype associated with DNA-negative mutants characterized by prolonged synthesis of early proteins and the absence of lateprotein synthesis, weak or slow late protein synthesis, and abortiveLate protein synthesis.
TL;DR: In this paper, the authors describe three mutant murine T-lymphosarcoma cell lines with altered dNTP pools and increased rates of spontaneous mutation to dexamethasone resistance and 6-thioguanine resistance.
Abstract: Recent studies of in vitro DNA synthesis have shown that fidelity of replication is influenced by the relative concentrations of deoxyribonucleoside triphosphates (dNTPs). Several investigators have used reconstituted prokaryotic replication systems to copy defined natural templates and have shown that specific incorporation errors can be induced by an appropriate bias of the precursor pools. The recent demonstration of mutator phenotypes among mutant Chinese hamster ovary cell lines with altered intracellular dNTP pools has allowed extension of the in vitro observations to eukaryotic replication and repair mechanisms. We describe here three mutant murine T-lymphosarcoma cell lines with altered dNTP pools and increased rates of spontaneous mutation to dexamethasone resistance and 6-thioguanine resistance. Unlike previously described mammalian cells with mutator phenotypes, these three lines have demonstrable defects in known structural gene products. Two of these cell lines are heterozygous for mutations affecting the M1 subunit of ribonucleoside diphosphate reductase; the other mutant is deficient in deoxycytidylate deaminase. In each cell line these mutations result in deranged endogenous dNTP pools and increased rates of spontaneous mutation, which are shown to be characteristic of the cell line and independent of the two genetic markers examined. Furthermore, normalization of the dNTP pools of the deaminase-deficient cells suppresses its mutator phenotype. Thus, abnormal dNTP pools seem to cause enhanced mutagenesis in mammalian cells.
TL;DR: The specificity of the oligonucleotide as a mutagen and as a hybridization probe provide a general method for producing site specific mutations in DNA cloned in plasmid vectors such as pBR322.
Abstract: A nonadecanucleotide has been used both as a site specific mutagen to introduce a T leads to A transversion mutation in the human beta-globin gene cloned in pBR322 as well as a probe to screen transformed colonies for the desired mutant. The specificity of the oligonucleotide as a mutagen and as a hybridization probe provide a general method for producing site specific mutations in DNA cloned in plasmid vectors such as pBR322.
TL;DR: Evidence suggests that the gene product in pf-27 is extrinsic to the radial spokes and is required for the specific in vivo phosphorylation of spoke polypeptides.
Abstract: In addition to the previously studied pf-14 and pf-1 loci in Chlamydomonas reinhardtii, mutations for another five genes (pf-17, pf-24, pf-25, pf-26, and pf-27) have been identified and characterized as specifically affecting the assembly and function of the flagellar radial spokes. Mutants for each of the newly identified loci show selective alterations for one or more of the 17 polypeptides in the molecular weight range of 20,000-130,000 which form the radial spoke structure. In specific instances the molecular defect has been correlated with altered radial spoke morphology. Biochemical analysis of in vivo complementation in mutant X wild-type dikaryons has provided indirect evidence that mutations for four of the five new loci (pf-17, pf-24, pf-25, and pf-26) reside in structural genes for spoke components. In the case of pf-24, the identity of the mutant gene product was supported by analysis of induced intragenic revertants. In contrast to the other radial spoke mutants thus far investigated, evidence suggests that the gene product in pf-27 is extrinsic to the radial spokes and is required for the specific in vivo phosphorylation of spoke polypeptides.
TL;DR: Intracellular recordings of action potentials were made from the cervical giant axon in Shaker (Sh) mutants and normal Drosophila, and gel electrophoresis failed to detect an abnormal protein, suggesting that, if Sh codes for a nervous system protein, it is rare.
Abstract: Intracellular recordings of action potentials were made from the cervical giant axon in Shaker (Sh) mutants and normal Drosophila. The mutants showed abnormally long delays in repolarization. The defect is not due to abnormal Ca2+ channels, because it persists in the presence of Co2+, a Ca2+-channel blocker. On the other hand, the K+-channel blocker 4-aminopyridine causes a similar effect in normal animals, suggesting that the Sh mutant may have abnormal K+ conductance. Gene-dosage analysis of Sh shows that the defect is not due to underproduction of an otherwise normal molecule; it may be due to an abnormal molecule produced by the mutated gene. Gel electrophoresis failed to detect an abnormal protein, suggesting that, if Sh codes for a nervous system protein, it is rare. Genetic analysis of the Sh locus indicates three regions. Mutations or chromosome breaks in the two flanking regions cause Sh mutant physiology; the central region shows a “haplolethal effect”—i.e., heterozygous females are lethal.
TL;DR: It is shown that the precursor accumulating in the pep4-3 mutant is not produced in a doubly mutant strain that also bears a mutation in the carboxypeptidase Y structural gene that eliminates production of carboxymatic activity, and that proteinase B is not essential for the maturation of the precursor in vivo.
Abstract: Carboxypeptidase Y, a vacuolar enzyme in Saccharomyces cerevisiae, is synthesized as a larger precursor whose apparent molecular mass is approximately 67,000 daltons. We have characterized a recessive mutation, pep4-3, that prevents maturation of this precursor. The accumulated precursor does not possess enzymatic activity. We have shown that the precursor accumulating in the pep4-3 mutant is not produced in a doubly mutant strain that also bears a mutation in the carboxypeptidase Y structural gene that eliminates production of carboxypeptidase Y. We have also shown that a nonsense fragment of carboxypeptidase Y is processed. Although there is evidence that proteinase B can catalyze the conversion of the precursor to a mature form in vitro, nonsense mutations in the structural gene for proteinase B, PRB1, do not affect the levels of carboxypeptidase Y activity, and strains bearing these mutations produce a carboxypeptidase Y of apparently normal size. Hence, proteinase B is not essential for the maturation of carboxypeptidase Y precursor in vivo. The pep4-3 mutation affects at least five vacuolar enzymes. This suggests that there is a processing event common to all of these enzymes.
TL;DR: A method which allows isolation of deletions within hybrid plasmids is described, and it is found that Tc R mutants are usually maintained within the cell recombined with the parental Tc S plasmid.
TL;DR: It appears that insertion of a transposable element near the 5' terminus of the structural gene can produce constitutive expression of a normally glucose-repressed enzyme.