We have used an immunoprecipitation-PCR cycle to isolate physically genomic DNA sequences that are bound by the fission yeast cdc10 gene product in an attempt to identify novel target genes. An essential gene, cdt1, has been isolated whose expression is cell cycle regulated in a cdc10 dependent manner. The cdt1 promoter contains a recognition site for a sequence specific DNA binding factor. The cdc10 gene product is a component of this factor. Ectopic expression of cdt1 can complement a temperature sensitive mutation of cdc10 at semipermissive temperature. Cells carrying a null allele of cdt1 are defective in DNA replication but initiate mitotic events, suggesting that cdt1 is essential for the normal dependency relationship of S-phase and mitosis.