Molecular Cloning and Characterization of a Novel Putative STE20-like Kinase in Guinea Pigs

Protein kinases play a key role in cell growth and differentiation. We have isolated the cDNA of a novel protein serine/threonine kinase (referred to as STE20-like kinase (SLK)) from a guinea pig liver cDNA library with a probe generated by a cloning approach based on the polymerase chain reaction. The encoded polypeptide (1231 amino acids,Mr141,079) contains all conserved subdomains characteristic of the protein serine threonine kinase family. A hemagglutinin-tagged SLK expressed artificially in COS7 cells was hyperphosphorylated by anisomycin. By Northern blot analysis, SLK mRNA was detected in all organs examined: brain, lung heart, liver, kidney, spleen, testis, and eosinophils. Sequence comparisons of its catalytic domain related SLK to p21-activated kinase family of protein serine/threonine kinases. Its noncatalytic domain comprises several intriguing structural features, including the acidic region and the nuclear targeting sequence. This noncatalytic domain exhibited no extended similarity with other proteins. Thus, SLK is a protein serine/threonine kinase which contains an unknown regulatory domain(s).