Control of DNA synthesis genes in fission yeast by the cell-cycle gene cdclO ⁺

IN the budding yeast Saccharomyces cerevisiae, cell-cycle control over DNA synthesis occurs partly through the coordinate expression in late Gl phase of many, if not all, of the genes required for DNA synthesis^1-3. A cis-acting hexamer element ACGCGT (an Mlul restiction site) is responsible for coordinating transcriptional regulation of these genes at the Gl/S phase boundary^1,4 and we have identified a binding activity, DSC1, that recognizes these sequences in a cell-cycle-dependent manner¹. In the distantly related fission yeast⁵ Schizosaccharomyces pombe only one of the known DNA synthesis genes, cdc22 ⁺, which encodes a subunit of ribonucleotide reductase, is periodically expressed in late Gl (ref. 6). The promoter region of cdc22 ⁺ has two Mlul sites and five related sequences, suggesting that similar controls over DNA synthesis genes could occur in fission yeast. We report here a binding activity in fission yeast that is very similar to DSC1 in budding yeast. We also show that the fission yeast cdc10 ⁺ gene product, which is required for Start and entry into S phase^7,8, is a component of this binding activity.