A mutation in SPC42, which encodes a component of the spindle pole body, results in production of two-spored asci in Saccharomyces cerevisiae

In the yeast Saccharomyces cerevisiae, SPC42 is an essential gene, which en codes one of the major components of the spindle pole body (SPB). We report on a mutation in the SPC42 gene (spc42-102) that results in a sporulation- specific defect. Mitotic growth of haploid and diploid spc42-102 strains is normal and both exhibit the same growth rates as the isogenic wild-type st rains. Many diploid spc42-102/spc42-102 cells undergo normal meiotic nuclea r divisions, producing four haploid nuclei. However, a significant fraction of meiotic spc42-102/spc42-102 cells contain two immature SPBs and aberran t nuclei that are not surrounded by a prospore membrane. Some 40% of the re sultant asci contain only two spores, while wild-type diploid cells almost always produce four-spored asci. Segregation of auxotrophic markers that ar e tightly linked to the centromere reveals that two-spore asci formed from spc42-102/spc42-102 diploid cells exclusively contain nonsister haploid spo res. Western analysis and measurements of the fluorescent signal from an Sp c42p-GFP (green fluorescent protein) fusion reveal that the mutant strain f ails to accumulate Spc42p at meiosis. Thus, our results suggest that insuff iciency of Spc42p during meiosis results in a pair of immature nonsister SP Bs that are not enclosed by prospore membrane.