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 fluorescence-activated cell sorting analysis and by analyzing the pattern of expression of the DNA polymerase alpha-primase complex. Wild-type cells and cells lacking one of the two principal regulators of meiosis, Ime1 and Ime2, were compared. We show that premeiotic DNA synthesis does not occur in ime1 Delta diploids, but does occur in ime2 Delta diploids with an 8-9 h delay. At late meiotic times, ime2 Delta diploids exhibit an additional round of DNA synthesis. Furthermore, we show that in wildtype cells the B-subunit of DNA polymerase alpha is phosphorylated during premeiotic DNA synthesis, a phenomenon that has previously been reported for the mitotic cell cycle. Moreover, the catalytic subunit and the B-subunit of DNA polymerase a are specifically degraded during spore formation. Phosphorylation of the B-subunit does not occur in ime1 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 division, although it is required for spore formation.