MCM1 IS REQUIRED TO COORDINATE G(2)-SPECIFIC TRANSCRIPTION IN SACCHAROMYCES-CEREVISIAE

In the budding yeast Saccharomyces cerevisiae, MCMI encodes an essenti al DNA-binding protein that regulates transcription of many genes in c ooperation,vith different associated factors, With the help of a condi tional expression system, we show that Mcm1 depletion has a distinct e ffect on cell cycle progression by preventing cells from undergoing mi tosis. Genes that normally exhibit a G(2)-to-M-phase-specific expressi on pattern, such as CLB1, CLB2, CDCS, SW15, and ACE2, remain uninduced in the absence of functional Mcm1. In vivo footprinting experiments s how that Mcm1, in conjunction with an Mcm1-recruited factor, binds to the promoter regions of SW15 and CLB2 at sites shown to be involved in cell cycle regulation. However, promoter occupation at these sites is cell cycle independent, and therefore the regulatory system seems to operate on constitutively bound Mcm1 complexes. A gene fusion that pro vides Mcm1 with a strong transcriptional activation domain causes tran scription of SW15, CLB1, CLB2, and CDCS at inappropriate times of the cell cycle. Thus, Mcm1 and a cooperating, cell cycle-regulated activat ion partner are directly involved in the coordinated expression of mul tiple G(2)-regulated genes. The arrest phenotype of Mcm1-depleted cell s is consistent with low levels of Clb1 and Clb2 kinase. However, cons titutive CLB2 expression does not suppress the mitotic defect, and the refore other essential activities required for the G(2)-to-M transitio n must also depend on Mcm1 function.