We isolated a novel human cDNA, termed hCDC10, whose predicted product showed a high degree of homology to the CDC10 protein of Saccharomyces cerevisiae. This cDNA contained an open reading frame of 1254 nucleotides encoding 418 amino acids, which included a GTP-binding motif, GX4GKS--DX2G--KXD. The predicted peptide sequence also revealed partial amino-acid identity (40-50%) with Diff 6 in Drosophila and with H5 in mouse. Each of these sequence homologues, including Saccharomyces cerevisiae CDC10, contains the GTP-binding motif. Northern blot analyses indicated that the hCDC10 gene is expressed ubiquitously in normal tissues.