MCB elements and the regulation of DNA replication genes in yeast

In eukaryotic organisms, genes involved in DNA replication are often subject to some form of cell cycle control. In the yeast Saccharomyces cerevisiae, most of the DNA replication genes that have been characterized to date are regulated at the transcriptional level during G1 to S phase transition. A cis-acting element termed the MluI cell cycle box (or MCB) conveys this pattern of regulation and is common among more than 20 genes involved in DNA synthesis and repair. Recent findings indicate that the MCB element is well conserved among fungi and may play a role in controlling entry into the cell division cycle. It is evident from studies in higher systems, however, that transcriptional regulation is not the only form of control that governs the cell-cycle-dependent expression of DNA replication genes. Moreover, it is unclear why this general pattern of regulation exists for so many of these genes in various eukaryotic systems. This review summarizes recent studies of the MCB element in yeast and briefly discusses the purpose of regulating DNA replication genes in the eukaryotic cell cycle.