Dual functions of CDC6: a yeast protein required for DNA replication also inhibits nuclear division.

Abstract

The Saccharomyces cerevisiae gene CDC6, whose protein product is required for DNA replication, is transcribed only in late G1 and S phases. We have discovered a critical reason why CDC6 expression is regulated in this fashion. Constitutive CDC6 transcription greatly delayed the initiation of M phase without effecting the G1-S transition or growth rate. This occurred in both fission and budding yeasts. The CDC6-induced M phase delay was dependent on the wee1/mik1 mitotic inhibitor kinases and was greatly accentuated in strains defective for the cdc25/MIH1 mitotic inducer phosphatases, indicating that CDC6 indirectly inhibits activation of the p34cdc2/CDC28 M phase kinase. Thus CDC6 appears to have an important and perhaps unique dual role in S phase, it is first required for the initiation of DNA replication and then actively participates in the suppression of nuclear division.