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R Egel

Publications and source records attributed to R Egel.

At least 19 recordsLinked to original sources
PubMed1995

Two-step activation of meiosis by the mat1 locus in Schizosaccharomyces pombe.

The mat1 locus is a key regulator of both conjugation and meiosis in the fission yeast Schizosaccharomyces pombe. Two alternative DNA segments of this locus, mat1-P and mat1-M, specify the haploid cell types (Plus and Minus). Each segment includes two genes: mat1-P includes mat1-Pc and mat1-Pm, while mat1-M includes mat1-Mc and mat1-Mm. The mat1-Pc and mat1-Mc genes are responsible for establishing the pheromone communication system that mediates conjugation between P and M cells, while all four mat1 genes are required for meiosis in diploid P/M cells. Our understanding of the initiation of meiosis is based largely on indirect observations, and a more precise investigation of these events was required to define the interaction between the mat1 genes. Here we resolve this issue using synthetic pheromones and P/M strains with mutations in either mat1-Pc or mat1-Mc. Our results suggest a model in which the mat1 locus plays two roles in controlling meiosis. In the first instance, the mat1-Pc and mat1-Mc functions are required to produce the mating pheromones and receptors that allow the generation of a pheromone signal. This signal is required to induce the expression of mat1-Pm and mat1-Mm. This appears to be the major pheromone-dependent step in controlling meiosis since ectopic expression of these genes allows meiosis in the absence of mat1-Pc and mat1-Mc. The mat1-Pm and mat1-Mm products complete the initiation of meiosis by activating transcription of the mei3 gene.

Base Sequence↗
PubMed1992

The ras1 function of Schizosaccharomyces pombe mediates pheromone-induced transcription.

Loss of ras1+ function renders fission yeast cells unable to undergo morphological changes in response to mating pheromones, whereas cells carrying activated mutations in ras1 are hyper-responsive. This has led to the suggestion that the ras1 gene product plays a role in mating pheromone signal transduction. Using partially purified M factor we demonstrate that the mat1-Pm gene, which controls entry into meiosis, is transcribed in response to a pheromone signal. Strains mutated in the ras1 gene or in ste6, the fission yeast homologue of Ras protein GDP/GTP exchange factor, are unable to induce transcription of mat1-Pm in response to M factor. Furthermore, an activated ras1val17 mutant exhibits a stronger induction of the mat1-Pm transcript. However, transcription still depends on nitrogen deprivation as well as on the presence of pheromone, showing that activation of the Ras1 protein alone does not substitute for any of these signals. The pat1-114 mutant bypasses the ras1/ste6 checkpoint, suggesting that activation of ras1 contributes to inactivation of the pat1 protein kinase.

Blotting, Northern↗
PubMed1992

Functional conservation between Schizosaccharomyces pombe ste8 and Saccharomyces cerevisiae STE11 protein kinases in yeast signal transduction.

In fission yeast (Schizosaccharomyces pombe), the mat1-Pm gene, which is required for entry into meiosis, is expressed in response to a pheromone signal. Cells carrying a mutation in the ste8 gene are unable to induce transcription of mat1-Pm in response to pheromone, suggesting that the ste8 gene product functions in the signal transduction pathway. The ste8+ gene encodes a 659 amino acid putative protein kinase, which is identical to the previously identified byr2 suppressor of the ras1 defect. Furthermore, ste8+ is highly homologous to the Saccharomyces cerevisiae STE11 gene, which functions in signal transduction in budding yeast. Expression of the S. cerevisiae STE11 gene in S. pombe ste8 mutants restores the ability to transcribe mat1-Pm in response to pheromone. Also, such cells become capable of conjugation and sporulation. When mat1-Pm is artifically expressed from a heterologous promoter, ste8 mutant cells will enter meiosis. This demonstrates that the meiotic defect of ste8 mutants is due to the absence of the mat1-Pm gene product.

Amino Acid Sequence↗
PubMed1991

New vectors in fission yeast: application for cloning the his2 gene.

We describe a new Escherichia coli vector (pON5) that allows positive selection for recombinant clones. In this plasmid, the bla gene from pBR322 is permanently active, whereas the neo gene from transposon Tn5 is repressed by the cI-encoded lambda repressor. When DNA is inserted into the Bc/I or HindIII restriction sites situated within the cI gene, the neo gene becomes transcribed from the lambda pR promoter. We have also made a Schizosaccharomyces pombe derivative of pON5 (= pON163) by introducing the fission yeast ars1 and ura4+ sequences. We show that this plasmid is capable of transforming Sc. pombe ura4 strains, as well as ura 3 strains of the distantly related budding yeast Saccharomyces cerevisiae. We have used pON163 for the construction of two fission yeast genomic libraries. From these gene banks clones were isolated that were able to complement fission yeast his2 mutants. Such plasmids could also rescue his4C mutants of Sa. cerevisiae, defective in the histidinol dehydrogenase activity of the multifunctional HIS4 gene product. Finally, we describe the plasmid pDW232 which is useful for functional analysis of fission yeast genes. It is a pGEM3 derivative adapted to fission yeast, carrying multiple cloning sites between the T7 and SP6 promoters, together with ars1 and ura4+ from Sc. pombe.

Cloning, Molecular↗
PubMed1991

Pheromone production and response in sterile mutants of fission yeast.

Genetically heterothallic strains of various sterile mutants were assayed for residual production of the corresponding mating pheromone as well as responsiveness towards the opposite pheromone. No sexual activities were detected in ste11 strains (previously referred to as aff1 or steX, which we show are allelic), whilst the production of M factor was unaffected by ste1 to ste10 mutations. P factor production was still possible in class I ste mutants (ste5, ste6 and ste10), which also allow meiosis in diploid strains. With the exception of the leaky ste10-F23 mutant, no changes in cell morphology were induced by exposure to the opposite pheromone in the ste mutant strains.

Alleles↗
PubMed1990

The pat1 protein kinase controls transcription of the mating-type genes in fission yeast.

The developmental programme of fission yeast brings about a transition from mitotic cell division to the dormant state of ascospores. In response to nitrogen starvation, two cells of opposite mating type conjugate to form a diploid zygote, which then undergoes meiosis and sporulation. This differentiation process is characterized by a transcriptional induction of the mating-type genes. Conjugation can also be induced in pat1-ts mutants by a shift to a semi-permissive temperature. The pat1 gene encodes a protein kinase, which also functions further downstream in the developmental pathway controlling entry into meiosis. We have analysed transcriptional induction of mating-type genes in various strains--with and without a pat1-ts allele. In wild-type cells of P-mating type derepression occurs in two rounds. First, the mat1-Pc gene is induced in response to nitrogen starvation. Mutants in the map1 gene are defective in this process. In the following step the mat1-Pm gene is expressed in response to a pheromone signal generated by cells of M mating type. Both these controls are derepressed in the pat1-ts mutant at semipermissive temperature. Previous work has established that expression of the mating-type genes in the zygote leads to complete loss of pat1 protein kinase activity causing entry into meiosis. Thus, pat1 can promote its own inactivation. We suggest a model according to which a stepwise inactivation of pat1 leads to sequential derepression of the processes of conjugation and meiosis.

Conjugation, Genetic↗
PubMed1990

Choreoathetosis after deep hypothermia without circulatory arrest.

In 8 of 758 patients undergoing an intracardiac operation under cardiopulmonary bypass and hypothermia, choreoathetosis developed 3 to 7 days postoperatively. Before the onset of choreoathetosis, varying degrees of neurological dysfunction were noted. Electroencephalography and neuroimaging failed to detect any responsible functional or structural changes. Six patients are alive 1 to 3 years postoperatively, and their condition is improving. Two patients died of aspiration or sepsis. All patients were grouped based on factors identified as being possibly causative: depth of hypothermia, cooling time, flow rate, and repeated hypothermia. The incidence of choreoathetosis was significantly different in group A (rectal temperature greater than 25 degrees C) compared with group B (rectal temperature less than or equal to 25 degrees C) (0/295 versus 8/463; p = 0.02). Based on cooling time, the incidence of choreoathetosis was significantly different in group B1 (cooling time less than 1 hour) compared with group B2 (cooling time greater than or equal to 1 hour) (1/220 versus 7/243; p = 0.05). Based on flow rate during cooling, group B2 was further divided into the low-flow group (less than 1,500 mL.min-1.m-2) and the high-flow group (greater than or equal to 1,500 mL.min-1.m-2). Although not significant, the incidence of choreoathetosis was higher in the high-flow group (6/153 versus 1/90; p = 0.22). In group B patients having reoperation, the incidence of choreoathetosis was higher than in patients operated on for the first time (5/54 versus 3/409; p less than or equal to 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Athetosis↗
PubMed1990

Sexual differentiation in fission yeast.

The regulation of sexual reproduction in yeast constitutes the highest level of differentiation observed in these unicellular organisms. The various ramifications of this system involve DNA rearrangement, transcriptional control, post-translational modification (such as protein phosphorylation) and receptor/signal processing. A few basic similarities are common to both fission and budding yeasts. The wiring of the regulatory circuitry, however, varies considerably between these divergent yeast groups.

Conjugation, Genetic↗
PubMed1989

Mapping the double-strand breaks at the mating-type locus in fission yeast by genomic sequencing.

In fission yeast mating-type switching is initiated by the formation of a double-strand DNA break at the mating-type locus. A prerequisite for generation of the break is some 'imprinting' of the DNA in the previous cell cycle. We have used the technique of genomic sequencing to map the position of the break directly on chromosomal DNA cleaved in vivo. On one strand the break is situated very close to the right-hand border of the expressed mat1 cassette. Cells of opposite mating type, P and M, have their breaks at slightly different positions on this strand. On the other DNA strand of both alleles the ends are probably masked by tightly bound proteins and therefore the precise nature of the break could not be determined. Since the break is stable throughout the cell cycle, these proteins may function in vivo to confer structural stability on the chromosomes having the break. The implications of these findings for models of mating-type switching are discussed.

Base Sequence↗
PubMed1984

Genes required for initiation and resolution steps of mating-type switching in fission yeast.

The fission yeast Schizosaccharomyces pombe switches mating type by transposition of a copy of DNA derived from either of the two storage cassettes, mat2 -P and mat3 -M, into the expression locus, mat1 . The recombinational event of switching is initiated by a double-stranded DNA break present in approximately 20% of the molecules at mat1 . Fifty-three mutants defective in switching of mating type have been isolated previously, and each has been assigned to 1 of 10 linkage groups. One group consists of cis-acting mutations at mat1 , which reduce the amount of the DNA double-strand cut. The remaining nine groups are mutations in genes that are unlinked to the mating-type locus and are studied here. Three ( swi1 , -3, -7) are required for formation of the double-strand cut, whereas the others are not. Mutants of three genes ( swi4 , -8, -9) undergo high-frequency rearrangement of the mating-type locus indicative of errors of resolution of recombinational intermediates. The remaining three ( swi2 , -5, -6) have normal levels of cut, do not make errors of resolution, and possibly are required either for efficient utilization of the cut or determining the directionality of switching. The data suggest that the switching process can be dissected into genetically distinguishable steps.

Ascomycota↗