cDNA cloning and characterization of rat Clk3, a LAMMER kinase predominately expressed in testis

A cDNA clone of a protein kinase with high similarity to the Clk (Cdc2-like kinases) subfamily was isolated from a rat brain library and characterized. Its deduced amino acid sequence exhibited a 99% identity with human Clk3 and was therefore designated rat Clk3. In addition to the protein kinase domain, the sequence (490 amino acids) comprises an N-terminal domain with a strikingly high portion of basic amino acids. A glutathione S-transferase fusion protein of Clk3 catalyzed autophosphorylation of the kinase but not phosphorylation of the exogenous substrates histone or casein. By Northern blot analysis of different rat tissues, mRNA of Clk3 was detected predominately in testis, suggesting that this kinase regulates a predominately testicular function.