The fission yeast cdc18+ gene product couples S phase to START and mitosis.

Commitment to the cell cycle in fission yeast requires the function of the cdc10+ transcriptional activator at START. The product of the cdc18+ gene is a major downstream target of cdc10+, and transcription of cdc18+ is activated by cdc10+ during passage through START. The cdc18+ function is required for entry into S phase. In addition, the product of the cdc18+ gene is part of the checkpoint control that prevents mitosis from occurring until S phase is completed. Thus, cdc18+ plays a key role in coupling S phase to START and mitosis.