Rad3-Cds1 mediates coupling of initiation of meiotic recombination with DNA replication - Mei4-dependent transcription as a potential target of meiotic checkpoint

Premeiotic S-phase and meiotic recombination are known to be strictly coupled in Saccharomyces cerevisiae. However, the checkpoint pathway regulating this coupling has been largely unknown. In fission yeast, Rad3 is known to play an essential role in coordination of DNA replication and cell division during both mitotic growth and meiosis. Here we have examined whether the Rad3 pathway also regulates the coupling of DNA synthesis and recombination. Inhibition of premeiotic S-phase with hydroxyurea completely abrogates the progression of meiosis, including the formation of DNA double-strand breaks (DSBs). DSB formation is restored in rad3 mutant even in the presence of hydroxyurea, although repair of DSBs does not take place or is significantly delayed, indicating that the subsequent recombination steps may be still inhibited. Examination of the roles of downstream checkpoint kinases reveals that Cds1, but not Chk1 or Mek1, is required for suppression of DSB in the presence of hydroxyurea. Transcriptional induction of some rec(+) genes essential for DSB occurs at a normal timing and to a normal level in the absence of DNA synthesis in both the wild-type and cds1 Delta cells. On the other hand, the transcriptional induction of the mei4(+) transcription factor and cdc25(+) phosphatase, which is significantly suppressed by hydroxyurea in the wild-type cells, occurs almost to a normal level in cds1 Delta cells even in the presence of hydroxyurea. These results show that the Rad3-Cds1 checkpoint pathway coordinates initiation of meiotic recombination and meiotic cell divisions with premeiotic DNA synthesis. Because mei4(+) is known to be required for DSB formation and cdc25(+) is required for activation of meiotic cell divisions, we propose an intriguing possibility that the Rad3-Cds1 meiotic checkpoint pathway may target transcription of these factors.