SSP1, A GENE NECESSARY FOR PROPER COMPLETION OF MEIOTIC DIVISIONS ANDSPORE FORMATION IN SACCHAROMYCES-CEREVISIAE

During meiosis, a diploid cell undergoes two rounds of nuclear divisio n following one round of DNA replication to produce four haploid gamet es. In yeast, haploid meiotic products are packaged into spores. To ga in new insights into meiotic development and spore formation, we follo wed differential expression of genes in meiotic versus vegetatively gr owing cells in the yeast Saccharomyces cerevisiae. Our results indicat e that there are at least five different classes of transcripts repres enting genes expressed at different stages of the sporulation program. Here we describe one of these differentially expressed genes, SSP1, w hich plays an essential role in meiosis and spore formation. SSP1 is e xpressed midway through meiosis, and homozygous ssp1 diploid cells fai l to sporulate. In the ssp1 mutant, meiotic recombination is normal bu t viability declines rapidly. Both meiotic divisions occur at the norm al time; however, the fraction of cells completing meiosis is signific antly reduced, and nuclei become fragmented soon after meiosis II. The ssp1 defect does not appear to be related to a microtubule-cytoskelet al-dependent event and is independent of two rounds of chromosome segr egation. The data suggest that Ssp1 is likely to function in a pathway that controls meiotic nuclear divisions and coordinates meiosis and s pore formation.