PUTATIVE NEW-PROTEIN KINASE ASSOCIATED WITH MICROTUBULES IN MAMMALIAN-CELLS

Using an expression vector cDNA library of cultured Chinese hamster ce lls(CHO), cDNA corresponding to a 618-residue C-terminal fragment of p rotein p3D2 (fp3D2) has been isolated. This protein is homologous with the putative human KIAA0204 and rat RatSK2 protein kinases [EC 2.7.1. 37]. The C-terminal parts of KIAA0204, RatSK2, and fp3D2 contain a reg ion similar in sequence to fibrillar cytoskeletal proteins. Antibodies against fused fp3D2 produced in Escherichia coli recognized on immuno blots a 210-kDa polypeptide in the CHO cells and both 250- and 210-kDa polypeptides in cultured human, porcine, and murine cells. In immunof lorescence microscopy, the antibodies revealed microtubules and nuclei in all the cells. In cell homogenates, the antibodies reacted with th e 210-kDa polypeptide, which is best expressed in tissues rich in micr otubules, i.e., brain and adrenal and seminal glands. Thus, KTAA0204, RatSK2 and p3D2 appear to be species-specific variants or close isofor ms of one protein, a putative protein kinase which is ubiquitous in ma mmalian cells and is associated with microtubules.