The complete nucleotide sequence of a 2.9-kb DNA fragment containing the CDC2 gene-complementing activity from Schizosaccharomyces pombe has been determined. Within this region lies a 1.69-kb DNA sequence whose predicted amino acid sequence shows extensive homology to that previously deduced for the CDC28 gene product from Saccharomyces cerevisiae [Lörincz and Reed, Nature 307 (1984) 183-185]. Taken with the earlier observation that mutants in CDC2 can be rescued by the presence of the CDC28 gene [Beach, Durkacz and Nurse, Nature 300 (1982) 706-709], these results strongly suggest that the two genes code for similar functions. In contrast to the CDC28 gene, however, which contains no introns, the CDC2 coding sequence is split by four introns and from a comparison of the two sequences a consensus sequence for intron splicing in S. pombe can be established. Both CDC2 and CDC28 contain the consensus sequences for the ATP binding and phosphorylation acceptor sites of protein kinases such as bovine cAMP-dependent protein kinase (bov PK) and the src family of viral oncogene products.