Several members of the cdk family of protein kinases are involved in the regulation of the eukaryotic cell cycle. Using a PCR-based strategy we have screened different human tumor cell lines for cdk-related cDNAs. One clone isolated from the bladder carcinoma cell line RT112 encodes a novel protein kinase named PISSLRE, based on its predicted sequence at the conserved PSTAIRE motif. PISSLRE showed 50% amino acid identity with the previously isolated p58KGTA. PISSLRE contained all the structural elements featured by cyclin dependent kinases, including a proline in the PSTAIRE motif, which might be important for cyclin binding. PISSLRE was found expressed as 2.0 kb messenger RNA in a variety of human cell lines. Its expression was not restricted to tumor cells as it was detectable also in normal fibroblasts. In adult tissues, PISSLRE mRNA showed the highest expression in lung, liver and kidney. The broad expression pattern in adult tissues might suggest that PISSLRE could be involved in processes distinct from cell proliferation.