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Biomedical subjects

R Egel

Publications and source records attributed to R Egel.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1978

Synaptonemal complex and crossing-over: structural support or interference?

Positive cross-over interference is attributed to the prevention of crossing-over by the growing synaptonemal complex. This conjecture is based on a report in the literature that the selection of prospective cross-over sites may actually precede a proper synapsis of homologous chromosomes during meiotic prophase. A genetic test of this notion is suggested using a properly marked trisomic configuration, applicable to a variety of organisms.

Animals↗
PubMed1977

Selective spore survival during replica-plating of fission yeast.

Vegetative cells of Schizosaccharomyces pombe, upon exposure to acetone vapours, are inactivated at a faster rate than ascospores of this yeast. This observation has been used to develop a simple and fast method by which colonies can be replica-plated and only spores survive in the replicas. The colony patterns are exposed to acetone while still on the velvet used for replica-plating.

Acetone↗
PubMed1976

Rearrangements at the mating type locus in fission yeast.

Crosses involving the partially defective mating type mutant B102 (functional in conjugation, defective in meiosis) have confirmed the notion that, in Schizosaccharomyces pombe, certain mating type mutations can arise by transposition. A copy of the mat2P segment (specifying + mating type) is transposed and inserted into the mat1M segment (usually specifying - mating type). The mat1M segment affected by the insertion loses its former - function entirely. The - function is, however, fully regained upon excision of the transposed and inserted mat2P segment. At either position, the mat2P segments can undergo inactivations to different states of residual activity. These events can occur about as frequent as other mutations of the mating type locus (ca. 10(-4) per cell division). In certain diploid strains, such inactivations were significantly correlated with recombination. Spontaneous reversions to full activity were also observed.

Ascomycota↗
PubMed1976

The genetic instabilities of the mating type locus in fission yeast.

Certain genetic instabilities of the "mating type locus" in the yeast Schizosaccharomyces pombe are interpreted in terms of transposition: Homothallic strains are characterized by two adjacent mating type genes (mat1-mat2+) with sexually complementary functions. One of these genes (mat2+) is able to duplicate itself, and the duplicated copy maps at the position of mat1-. The former function of mat1-is lost (owing to insertion), and only becomes reactivated when the inserted sequence (mat1+) is again excised. Analyses of analogous instabilities expressed by the partially defective mutation mat2+ -B102 have substantiated this transposition scheme. Homothallism is acribed to alternate and mutually exclusive activation of mat1- or mat2+ genes.

Alleles↗