Rme1, which controls CLN2 expression in Saccharomyces cerevisiae, is a nuclear protein that is cell cycle regulated

In Saccharomyces cerevisiae commitment to cell division occurs at a point i n GI termed Start. This important transition is regulated by the cyclin-dep endent kinase Cdc28, in association with the GI cyclins Cln1, 2 and 3. Tran scription of the GI cyclins is induced by the transcription factor complexe s SBF (Swi4-Swi6) and MBF (Mbp1-Swi6); however, data suggest that other pro teins are also able to regulate their expression. We previously identified Rme1, a transcription factor with a well documented role in negatively regu lating IME1 expression and meiosis, as an activator of CLN2 transcription. We now show that Rme1 acts through two specific Rme1 response elements in t he CLN2 promoter to induce expression of the gene. We have analysed in deta il the timing of RME1 transcription at the end of mitosis and in G I, and t he roles of the transcription factors Ace2 and Swi5 in mediating this expre ssion. We also demonstrate that the Rme1 protein is cell cycle regulated, p eaking in Gl and appearing in the nucleus at this time. Finally, the role o f RME1 in cell cycle regulation is confirmed by the observation of periodic RME1 expression in diploid cells, where it has no IME1 repressor function, this finding emphasises its role in the regulation of CLN2 expression in G 1.