A MEIOSIS-SPECIFIC PROTEIN-KINASE, IME2, IS REQUIRED FOR THE CORRECT TIMING OF DNA-REPLICATION AND FOR SPORE FORMATION IN YEAST MEIOSIS

In this report we study the regulation of premeiotic DNA synthesis in Saccharomyces cerevisiae. DNA replication was monitored by fluorescenc e-activated cell sorting analysis and by analyzing the pattern of expr ession of the DNA polymerase alpha-primase complex. Wild-type cells an d cells lacking one of the two principal regulators of meiosis, Ime1 a nd Ime2, were compared. We show that premeiotic DNA synthesis does not occur in ime1 Delta diploids, but does occur in ime2 Delta diploids w ith an 8-9 h delay. At late meiotic times, ime2 Delta diploids exhibit an additional round of DNA synthesis. Furthermore, we show that in wi ldtype cells the B-subunit of DNA polymerase alpha is phosphorylated d uring premeiotic DNA synthesis, a phenomenon that has previously been reported for the mitotic cell cycle. Moreover, the catalytic subunit a nd the B-subunit of DNA polymerase a are specifically degraded during spore formation. Phosphorylation of the B-subunit does not occur in im e1 Delta diploids, but does occur in ime2 Delta diploids with an 8-9 h delay. In addition, we show that Ime2 is not absolutely required for commitment to meiotic recombination, spindle formation and nuclear div ision, although it is required for spore formation.