A ZINC-FINGER PROTEIN CONTROLS THE ONSET OF PREMEIOTIC DNA-SYNTHESIS OF FISSION YEAST IN A MEI2-INDEPENDENT CASCADE

In the fission yeast Schizosaccharomyces pombe, meiosis is initiated by the action of Mei2 in a complex cascade activated following conjugation. We have isolated a new gene named rep1(+) that is required for the initiation of premeiotic DNA synthesis. rep1(+) encodes a 53 kDa protein with one zinc finger motif that is essential for function, and effectively rescues a null mutant of the res1(+) gene but only partially a temperature-sensitive mutant of the cdc10(+) gene, both of which are required for the onset of mitotic, as well as premeiotic, S phase. Deletion of rep1(+) has no apparent effects on the mitotic cell cycle or conjugation, but blocks the initiation of premeiotic DNA synthesis. However, this defect is partially suppressed when rapidly growing cells are induced to conjugate, indicating that the rep1(+) function is at least partly substituted by those of the genes controlling the 'start' of the mitotic cell cycle. The rep1 null mutant fails to induce the res2(+) gene, a newly identified res1(+) homolog cooperating with Cdc10 and acting for the onset of mitotic and premeiotic DNA synthesis, as well as for meiotic division. The rep1(+) gene itself is induced moderately during nitrogen starvation but highly during conjugation, and this induction is dependent on both ste11(+) and mating pheromones but independent of mei2(+). Thus, rep1(+) controls the initiation of premeiotic DNA synthesis via induction and/or activation of Res2 and some other essential factors in a cascade independent of Mei2.