Genes controlling meiosis and spore formation in yeast.

PORULATION of diploids of Saccharomyces cerevisiae involves meiosis and subsequent ascospore formation. The genetic and physiological control of this process is of interest as a model system for the control of meiosis and gametogenesis and has been the subject of several reviews (FOWELL 1969; HABER and HALVORSON 1972; TINGLE et al. 1973). Study of meiosis and gamete formation at the biochemical, genetic, and cytological levels in several organisms has yielded a wealth of information. However, we still have relatively little knowledge of the nature and number of independent gene functions which control the events we observe and integrate them into a successful developmental sequence. Our primary objective has been to dissect the genetic control of meiosis and sporulation in yeast through the study of variants, mutant in gene functions indispensible for the completion of sporulation but which are capable of growth by mitosis and budding. We have thus attempted to restrict our attention to the properties of mutants defective in functions specific to meiosis and ascospore development. Both recessive (spo) and dominant (WO) temperature-sensitive sporulation-deficient mutants have been isolated and eleven loci have been identified among recessive spo mutants (ESPOSITO and ESPOSITO 1969; and ESPOSITO et al. 1972). Complementation studies suggest that approximately 50 loci coding functions indispensible for sporulation may be recovered (ESPOSITO et al. 1972). In this report we wish to describe recent progress in the characterization of spo mutants of ten loci and three dominant mutants. These studies provide information with respect to the stages of sporulation where development may terminate or become abnormal among mutants which fail to form typical ascospores at a restrictive temperature. Sporulation-deficient mutants of three loci (spol, sp02, and spo3) have been examined for both recombinational ability (ESPOSITO and ESPOSITO 1974) and fine structural development at the level of electron microscopy (MOENS, ESPOSITO and ESPOSITO 1974). These mutants demonstrate features of the integration and coordinate control of certain landmark events of meiosis and spore formation in yeast.