| Two mutations are described which alter certain features of mating and sporulation activity in the yeast Saccharomyces cerevisiae. The first mutation, the dmt (dual mating type) gene allows Mat (alpha) dmt cells to enter into otherwise prohibited mating with cells of the same mating type to form (alpha) mating, nonsporulating diploids.;The second mutation, the dominant ARM (active regulation of meiosis) gene allows the otherwise prohibited sporulation of diploid cells of the genotypes Mat (alpha)/Mat (alpha), Mat (alpha)/deletion of Mat and Mat (alpha)/mat a* (mat a* is a recessive mutation of the mat a locus. mat a*/Mat (alpha) diploids are unable to sporulate). Mat a/Mat a diploids carrying the ARM gene are unable to sporulate.;Mat (alpha) ARM strains show enhanced ability to undergo switch of mating type as compared to Mat (alpha) wild-type strains.;The ARM gene was used to study the nature of the dmt gene by allowing sporulation of the otherwise nonsporulating diploids produced by the mating of Mat (alpha) cry(,1)('s) dmt with Mat (alpha) cry(,1)('r) ARM. In this cross, 246 colonies, each the product of an independent mating event were examined. Tetrad analysis of sample colonies demonstrated the presence of four major classes of diploids defined by the following tetrad configurations:;dmt gene facilitated (alpha) x (alpha) matings result from deletion of mating locus information in Mat (alpha) dmt cells allowing these cells to mate as a mating type cells.;2 Mat (alpha) cry(,1)('r) : 2 nonviable.;4 Mat (alpha) cry(,1)('r).;2 Mat (alpha) cry(,1)('r) : 2 Mat (alpha) cry(,1)('S).;2 Mat (alpha) cry(,1)('r) : 2 Mat (alpha) cry(,1)('S).;This data also supports the model of dmt gene-facilitated rare matings where dmt induced loss of Mat (alpha) information allows a cell to mate as an a mating type cell. In addition, this data shows that dmt induced chromosomes III damage can be repaired with homologous information after mating has occurred.;The ARM gene, which was used to allow sporulation of diploids formed by dmt gene-facilitated rare matings, appears to be a cryptic copy of Mat a information located on the right arm of chromosome III, distal to thr(,4).;Another gene, ARM (alpha), is described which appears to be a cryptic form of Mat (alpha) information which is expressed in a manner analogous to the Mat a information of the ARM gene.;The ability of the ARM gene to replace HMRa in allowing homothallic switch of mating type is examined. |
