The Saccharomyces cerevisiae CLB5 promoter contains two middle sporulation elements (MSEs) that are differentially regulated during sporulation

The B-type cyclins Clb5 and Clb6 are essential activators of DNA replication during sporulation in Saccharomyces cerevisiae. The expression of CLB5 is maximally induced during the middle phase of sporulation by the transcription factor Ndt80. We have performed an analysis of the CLB5 promoter and have identified two middle sporulation elements (MSEs) that act as binding sites for Ndt80. Although both MSE sequences bind Ndt80 in vitro, they display differential effectiveness in their ability to function as cis-acting regulatory sequences in vivo. Mutation of both MSE sequences in the CLB5 promoter profoundly reduces the induction of CLB5 transcription during the middle phase of sporulation but results in no obvious defect in progression through meiosis and sporulation, implying that the Ndt80-dependent induction of CLB5 is not required for effective DNA replication or chromosome division. Copyright © 2008 John Wiley & Sons, Ltd.