INFLUENCE OF THE matl-M ALLELE ON MEIOTIC RECOMBINATION IN THE MATING-TYPE REGION OF SCHZZOSACCHAROMYCES POMBEl

ANGEHRN and GUTZ (1968) have shown that homozygosity for the matl-M allele in diploid strains of Schizosaccharomyces pombe increases mitotic recombination between his7 and mat2. In this paper, we report that meiotic recombination frequencies can vary from 3.4 to 16.1 percent between his7 and his2 and that this variation is due to the combination of alleles a t the mat i and mat2 loci. HE mating-type region of the fission yeast, Schizosaccharomyces pombe, Tcontains two mating-type loci, mat1 and mat2, which are separable by meiotic and mitotic recombination; these loci appear to regulate the sexual cycle (LEUPOLD 1958; GUTZ et al. 1974). ANGEHRN and Gum (1968 and unpublished) found that mitotic recombination in the mating-type region of S. pombe occurred more frequently when diploid strains were homozygous for matl-M (approximately 1 in 45 cell divisions) than for any other mating-type allele combinations. (For a discussion of the new mating-type terminology, see below). This increase in recombination was localized between his7 and mat2. In this paper we examine the influence of the mating-type genes on meiotic recombination in the same region. MATERIALS A N D METHODS Mating-type terminology: EGEL (1976) has recently suggested a new mating-type terminology for S. pombe. We use a modification of the system proposed by EGEL in that P (plus mating specificity) and M (minus mating specificity) are not used as superscripts of the gene symbols * This research was done while both authors were at the University of Texas at Dallas (Program in Biology) and were supported by National Science Foundation Grant GB-15148, by Grant GM-I9849 awarded by the Public Health Service and by the University of Texas at Dallas Research Fund. 2 To whom requests for reprints should be sent. Genetus 88: 235-238 February, 1978. 236 J. H. MEADE A N D H. GUTZ TABLE 1 Mating-type terminology* Mating-type Old genotype symbols New genotype symbols+ h90 (homothallic) matlmat2+ matl-M mat2-P hfN (heterothallic+) mail+ mat2+ matl-P mat2-P h-S (heterothallic-) m a t t mat2" matl-M mat2-0 0 * Only those mating-types are shown which were used in the present experiments. t The allele designations M and P represent alleles of opposite heterothallic function, whereas represents a nonfunctional o r deleted gene. but follow these after a hyphen; the mating types and the new symbols for their genotypes are summarized in Table 1. Strains: The four strains used in these experiments are AH1 (his7 matl-P mat2-P), AH1-I (his7 matl-M mat2-P), SG393 (matl-M mat2-0 his2 aded-MZ10) and 9C (matl-P mat2-P his2 aded-M210). AHI-1 is a spontaneous mating-type mutant isolated from AH1. Strain 9 c was constructed in three steps. First, AH1 was crossed with SG393, asci were dissected, and a n h f N strain that did not require histidine was selected (+ matl-P milt2-P +). Second, this h + N strain was crossed with SG393, asci were dissected, and a strain with the genotype of Qc was selected. Third, this h + N strain (matl-P mat2-P his2 aded-M210) was backcrossed 8 time5 with SG393, so that the genetic background of 9C, except for the mating type, would be isogenic with SG393. The markers his7 and his2 flank the mating-type region (chromosome ZI), whereas aded maps on chromosome ZIZ (Table 2). Media and other experimental techniques: The media and experimental techniques have been described elsewhere (GUTZ et al. 1974). TABLE 2 Recombination between his7 and his2 Cross tetrads with four germinated spores' Segregation of his7 and hisal. cross Genotype Number PD NPD TT Map distance$ (a) AH1 his7 matl-P mat2-P + +