Genetics

Nelson, O E

doi: 10.1093/genetics/135.4.937pmid: 8307333

Article PDF first page preview Close This content is only available as a PDF. © Genetics 1993 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Hirsch, J P; Cross, F R

doi: 10.1093/genetics/135.4.943pmid: 8307334

Abstract Dominant mutations at the DAF2 locus confer resistance to the cell-cycle arrest that normally occurs in MATa cells exposed to alpha-factor. One of these alleles, DAF2-2, has also been shown to suppress the constitutive signaling phenotype of null alleles of the gene encoding the alpha subunit of the G protein involved in pheromone signaling. These observations indicate that DAF2-2 inhibits transmission of the pheromone response signal. The DAF2-2 mutation has two effects on the expression of a pheromone inducible gene, FUS1. In DAF2-2 cells, FUS1 RNA is present at an increased basal level but is no longer fully inducible by pheromone. Cloning of DAF2-2 revealed that it is an allele of STE3, the gene encoding the a-factor receptor. STE3 is normally an alpha-specific gene, but is inappropriately expressed in a cells carrying a STE3DAF2-2 allele. The two effects of STE3DAF2-2 alleles on the pheromone response pathway are the result of different functions of the receptor. The increased basal level of FUS1 RNA is probably due to stimulation of the pathway by an autocrine mechanism, because it required at least one of the genes encoding a-factor. Suppression of a null allele of the G alpha subunit gene, the phenotype associated with the inhibitory function of STE3, was independent of a-factor. This suppression was also observed when the wild-type STE3 gene was expressed in a cells under the control of an inducible promoter. Inappropriate expression of STE2 in alpha cells was able to suppress a point mutation, but not a null allele, of the G alpha subunit gene. The ability of the pheromone receptors to block the pheromone response signal in the absence of the G alpha subunit indicates that these receptors interact with another component of the signal transduction pathway. This content is only available as a PDF. © Genetics 1993 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Reijo, R A; Cho, D S; Huffaker, T C

doi: 10.1093/genetics/135.4.955pmid: 8307335

Abstract rts1-1 was identified as an extragenic suppressor of tub2-104, a cold-sensitive allele of the sole gene encoding beta-tubulin in the yeast, Saccharomyces cerevisiae. In addition, rts1-1 cells are heat sensitive and resistant to the microtubule-destabilizing drug, benomyl. The rts1-1 mutation is a deletion of approximately 5 kb of genomic DNA on chromosome X that includes one open reading frame and three tRNA genes. Dissection of this region shows that heat sensitivity is due to deletion of the open reading frame (HIT1). Suppression and benomyl resistance are caused by deletion of the gene encoding a tRNA(Arg)AGG (HSX1). Northern analysis of rts1-1 cells indicates that HSX1 is the only gene encoding this tRNA. Deletion of HSX1 does not suppress the tub2-104 mutation by misreading at the AGG codons in TUB2. It also does not suppress by interfering with the protein arginylation that targets certain proteins for degradation. These results leave open the prospect that this tRNA(Arg)AGG plays a novel role in the cell. This content is only available as a PDF. © Genetics 1993 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Toyn, J H; Johnston, L H

doi: 10.1093/genetics/135.4.963pmid: 8307336

Abstract The DBF2 and DBF20 genes of the budding yeast Saccharomyces cerevisiae encode a pair of structurally similar protein kinases. Although yeast with either gene deleted is viable, deletion of both genes is lethal. Thus, the Dbf2 and Dbf20 proteins are functional alternatives for an essential activity. In contrast to deletions, four different mutant alleles of DBF2 are lethal. Thus, the presence of a nonfunctional Dbf2 protein, rather than the lack of function per se, is inhibitory. Here we present genetic evidence that nonfunctional mutant Dbf2 protein blocks the function of Dbf20 protein by sequestering a common interacting protein encoded by SPO12. Even a single extra copy of SPO12 is sufficient to suppress the dbf2 defect. Since SPO12 appears to encode a limiting factor, it may be a rate limiting cofactor that is involved in the regulation of the Dbf2 and Dbf20 protein kinases. A corollary to the finding that one extra copy of SPO12 can suppress dbf2, is that the acquisition of an extra chromosome VIII, which carries the SPO12 locus, will also suppress dbf2. Indeed, physical analysis of chromosome copy number in dbf2 revertants able to grow at 37 degrees showed that the frequency of chromosome VIII acquisition increased when cells were incubated at the restrictive temperature, and reached a frequency of more than 100-fold the amount in wild-type yeast. This suggested that the dbf2 mutation was not only suppressed by an extra copy of chromosome VIII but also that the dbf2 mutation actually caused aberrant chromosomal segregation. Conventional assays for chromosome loss confirmed this proposal. This content is only available as a PDF. © Genetics 1993 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Hastings, P J; McGill, C; Shafer, B; Strathern, J N

doi: 10.1093/genetics/135.4.973pmid: 8307337

Abstract Integration of linearized plasmids into yeast chromosomes has been used as a model system for the study of recombination initiated by double-strand breaks. The linearized plasmid DNA recombines efficiently into sequences homologous to the ends of the DNA. This efficient recombination occurs both for the configuration in which the break is in a contiguous region of homology (herein called the ends-in configuration) and for "omega" insertions in which plasmid sequences interrupt a linear region of homology (herein called the ends-out configuration). The requirements for integration of these two configurations are expected to be different. We compared these two processes in a yeast strain containing an ends-in target and an ends-out target for the same cut plasmid. Recovery of ends-in events exceeds ends-out events by two- to threefold. Possible causes for the origin of this small bias are discussed. The lack of an extreme difference in frequency implies that cooperativity between the two ends does not contribute to the efficiency with which cut circular plasmids are integrated. This may also be true for the repair of chromosomal double-strand breaks. This content is only available as a PDF. © Genetics 1993 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Staples, R R; Dieckmann, C L

doi: 10.1093/genetics/135.4.981pmid: 8307338

Abstract Mitochondrial biogenesis is dependent on both nuclearly and mitochondrially encoded proteins. Study of the nuclearly encoded mitochondrial gene products and their effect on mitochondrial genome expression is essential to understanding mitochondrial function. Mutations in the nuclear gene CBP1 of Saccharomyces cerevisiae result in degradation of mitochondrially encoded cytochrome b (cob) RNA; thus, the cells are unable to respire. Putative roles for the CBP1 protein include processing of precursor RNA to yield the mature 5' end of cob mRNA and/or physical protection of the mRNA from degradation by nucleases. To examine the activity of CBP1, we generated temperature-sensitive cbp1 mutant strains by polymerase chain reaction (PCR) mutagenesis and in vivo recombination. These temperature-sensitive cbp1 strains lack cob mRNA only at the nonpermissive temperature. Quantitative primer extension analyses of RNA from these strains and from a cbp1 deletion strain demonstrated that CBP1 is required for the stability of precursor RNAs in addition to production of the stable mature mRNA. Thus, CBP1 is not involved solely in the protection of mature cob mRNA from nucleases. Moreover, we found that mature mRNAs are undetectable while precursor RNAs are reduced only slightly at the nonpermissive temperature. Collectively, these data lead us to favor a hypothesis whereby CBP1 protects cob precursor RNAs and promotes the processing event that generates the mature 5' end of the mRNA. This content is only available as a PDF. © Genetics 1993 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Yang, X; Griffiths, A J

doi: 10.1093/genetics/135.4.993pmid: 8307339

Abstract We have discovered that, in certain crosses of natural isolates of Neurospora intermedia, linear and circular mitochondrial plasmids of the maternal parent are not transmitted to the progeny. This contrasts with the maternal transmission of organellar genetic elements generally observed in crosses between laboratory strains and between other natural isolates. Formally, failure of plasmid transmission is a type of plasmid suppression. The present cases represent the first report of plasmid suppressors in natural populations of fungi. Strains used as female parents can transmit or not transmit plasmids depending on the strain used as male parent. Males that act to suppress in one cross fail to suppress in others. Therefore, the suppression of plasmids depends on a strain-specific interaction and is not determined exclusively by the males. Since suppression is a specific interaction we inferred that it must be genetically based and tested this hypothesis by seeking segregation of suppressed and nonsuppressed phenotypes in octads. Segregation of the original full suppression of all plasmids was indeed observed in each of the three sets of testcrosses examined. The interaction type of suppression must be initiated in ascogenous tissue during the sexual cycle. It is a nonautonomous type of suppression, affecting all descendent cells. In any one case of suppression, either one, several, or all plasmids can be lost. Both linear and circular plasmids can be eliminated by the same suppressor genotype. In addition, several strains were found to contain suppressors that act after ascospore delineation. This autonomous type of suppression has been observed previously in laboratory strains, but not in natural isolates. All the cases of plasmid suppression identified in this study involved a range of apparently neutral circular and linear plasmids. Using one senescent Kalilo strain of N. intermedia, we did not detect any case of suppression of the senescence-determining linear plasmid kalDNA. This content is only available as a PDF. © Genetics 1993 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Ebert, R H; Cherkasova, V A; Dennis, R A; Wu, J H; Ruggles, S; Perrin, T E; Shmookler Reis, R J

doi: 10.1093/genetics/135.4.1003pmid: 8307318

Abstract We have used chromosome mapping with polymorphic markers to define genetic components governing life span in the nematode Caenorhabditis elegans. A complex recombinant-inbred population was derived from an interstrain cross, yielding > 1000 genotypes, each a composite of homozygous segments from the two parental strains. Genotypes were analyzed for the last-surviving 1-5% of worms in aging cohorts, and for young controls, by multiplex polymerase chain reaction using polymorphic markers to distinguish the parental alleles. We identified five regions of the genome at which one parental allele was significantly enriched in long-lived subpopulations. At four of five loci, the same alleles were selected in aging cohorts maintained under two different conditions, implying that these genes determine life span in differing environments. This content is only available as a PDF. © Genetics 1993 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Maine, E M; Kimble, J

doi: 10.1093/genetics/135.4.1011pmid: 8307319

Abstract The glp-1 gene is essential for two cell interactions that control cell fate in Caenorhabditis elegans: induction of anterior pharynx in the embryo and induction of mitotic proliferation in the germ line. To identify other genes involved in these cell interactions, we have isolated suppressors of two temperature sensitive alleles of glp-1. Each of 14 recessive suppressors rescues both embryonic and germline glp-1(ts) defects. These suppressors are extragenic and define a set of six genes designated sog, for suppressor of glp-1. Suppression of glp-1 is the only obvious phenotype associated with sog mutations. Mutations in different sog genes show allele-specific intergenic noncomplementation, suggesting that the sog gene products may interact. In addition, we have analyzed a semidominant mutation that suppresses only the glp-1 germline phenotype and has a conditional feminized phenotype of its own. None of the suppressors rescues a glp-1 null mutation and therefore they do not bypass a requirement for glp-1. Distal tip cell function remains necessary for germline proliferation in suppressed animals. These suppressor mutations identify genes that may encode other components of the glp-1 mediated cell-signaling pathway or regulate glp-1 expression. This content is only available as a PDF. © Genetics 1993 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Lissemore, J L; Currie, P D; Turk, C M; Maine, E M

doi: 10.1093/genetics/135.4.1023pmid: 8307320

Abstract The glp-1 gene product mediates cell-cell interactions required for cell fate specification during development in Caenorhabditis elegans. To identify genes that interact with glp-1, we screened for dominant suppressors of two temperature-sensitive glp-1 alleles and recovered 18 mutations that suppress both germline and embryonic glp-1 phenotypes. These dominant suppressors are tightly linked to glp-1 and do not bypass the requirement for a distal tip cell, which is thought to be the source of a signal that is received and transduced by the GLP-1 protein. Using single-strand conformation polymorphism (SSCP) analysis and DNA sequencing, we found that at least 17 suppressors are second-site intragenic revertants. The suppressors, like the original glp-1(ts) mutations, are all located in the cdc10/SWI6/ankyrin domain of GLP-1. cdc10/SWI6/ankyrin motifs have been shown to mediate specific protein-protein interactions in other polypeptides. We propose that the glp-1(ts) mutations disrupt contact between GLP-1 and an as yet unidentified target protein(s) and that the dominant suppressor mutations restore appropriate protein-protein interactions. This content is only available as a PDF. © Genetics 1993 This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)