The periodically expressed TMP1 gene of Saccharomyces cerevisiae is subject to START-dependent and START-independent regulation.

The rate of transcription of the Saccharomyces cerevisiae gene encoding thymidylate synthase (TMP1) fluctuates periodically during the cell cycle. The simplest explanation for this pattern of expression is that transcription occurs during the late G1 and early S phases and does not occur during other stages of the cell cycle. In this report, however, we show that TMP1 is subject to regulation that results in at least three different levels of expression: essentially nondetectable expression during stationary phase (G0), moderate level expression in START-arrested growing cells (START-independent), and a high level of expression in proliferating cells (START-dependent). Our analysis also shows that upstream elements important for START-independent expression and required for START-dependent expression are located within a 37-base region.