As a preliminary step for studying the function and intracellular behavior of the product of the CDC23 gene, a cell cycle gene of Saccharomyces cerevisiae, we cloned the CDC23 gene and determined its nucleotide (nt) sequence. The nt sequence contains an open reading frame (ORF) of 1878 nt coding for a protein of 626 amino acids (aa). The CDC23 gene is expressed as a 2.4- to 2.5-kb major transcript. The putative protein product of the CDC23 gene has a potential Ca2(+)-binding site near its N terminus, and has four contiguous repeats of a consensus sequence consisting of 34 aa near its C terminus. Regions that can be regarded as consisting of repeats of the same consensus sequence were found in the published aa sequences of the products of three other yeast genes.