The full-length STK17B cDNA clone encodes a deduced 372-amino acid protein with a molecular mass of 42.34 kD. The putative kinase domain is located at the N terminus and contains all 11 subdomains conserved among ser/thr kinases. STK17A and STK17B share 59.7% amino acid identity. Northern blot analysis revealed that STK17B was expressed in various tissues, such as heart, placenta, liver, and pancreas, as different-sized transcripts, presumably due to differences in the 3-prime untranslated region. Transient transfection of COS-7 cells showed that STK17B localized in nuclei. Phosphorylates myosin light chains. Acts as a positive regulator of apoptosis.