The G1/S cyclin Cig2p during meiosis in fission yeast.

Cyclin-dependent kinases (CDKs) are important for both mitotic and meiotic cell cycles. In fission yeast, the major CDK, Cdc2p is involved in premeiotic DNA replication and in meiosis II. One of its partners, the mitotic cyclin Cdc13p is known to be required for meiosis, whereas there are no studies on the G1/S cyclin Cig2p. In this article, we have studied the regulation of the Cdc2p/Cdc13p and Cdc2p/Cig2p complexes during synchronous meiosis. We observed that Cdc2p/Cig2p kinase is activated in an unexpected biphasic manner, first at onset of premeiotic S phase and again during meiotic nuclear divisions. The role of Cig2p during meiosis was investigated using cig2-deleted strains that exhibit delays in onset of both S phase and meiotic divisions as well as an inefficient completion of MII. Furthermore, analysis of cig2 transcripts revealed a meiosis-specific regulation of cig2 expression during MI/MII dependent upon the Mei4p transcription factor leading to a different transcription start site at this stage of meiosis.