sds22 is a regulatory polypeptide of protein phosphatase-1 that is required for the completion of mitosis in both fission and budding yeast. We report here the cDNA cloning of a human polypeptide that is 46% identical to yeast sds22. The human homolog of sds22 consists of 360 residues, has a calculated molecular mass of 41.6 kDa and shows a tandem array of 11 leucine-rich repeat structures of 22 residues. Northern analysis revealed a major transcript of 1.39 kb in all 8 investigated human tissues. sds22 was detected by western analysis in both the cytoplasm and the nucleus of rat liver cells as a polypeptide of 44 kDa.