Spo1, a phospholipase B homolog, is required for spindle pole body duplication during meiosis in Saccharomyces cerevisiae

The SPO1 gene was cloned and shown to encode an early meiotic transcript sp ecifying a nuclear protein with extensive similarity to fungal and vertebra te phospholipase enzymes. Alteration of a conserved serine residue in the p utative phospholipase active site, and presence of the spo1-1 temperature-s ensitive mutation, which resides near this site, each result in loss of SPO 1 function. The phenotype of a complete deletion indicates that SPO1 is dis pensable for vegetative growth, premeiotic DNA synthesis and meiotic recomb ination. In contrast. it is required for Meiosis I (MI) and Meiosis II (MII ) chromosome segregation and spore formation. In a null mutant similar to 7 5% of cells arrest early at MI spindle pole body (SPB) duplication, similar to 20% arrest at MII, and similar to 5% arrest at spore formation. Progres sion beyond the first arrest point suggests the existence of functions part ially redundant to Spo1 and that Spo1 is required at multiple stages. At pr esent SPO1 is the only known gene required for SPB duplication in meiosis b ut not in mitosis. Its product may thus play a regulatory (rather than a st ructural) role in SPB function. The transcriptional program in the spo1 nul l is similar to the wild type early in meiosis but is significantly delayed at later stages of sporulation. A single gene, CWP1, was recovered as a mu lti-copy suppressor of the spo1 null. CWP1 encodes a cell wall protein with a glycolipid moiety. We propose that, when modified by other lipases, this moiety may substitute for the product(s) of Spo1p lipase activity in meios is. Based on the similarity of Spo1p to phospholipase B enzymes, its unique role in SPB duplication, and pleiotropic effects on MII, late gene express ion and spore formation, we propose that the Spo1 protein participates in a novel meiotic pathway that functions through the SPB to coordinate nuclear division with spore development.