A casein kinase-like kinase phosphorylates beta-tubulin and may be a microtubule-associated protein.
The hypothesis that casein kinase II (CKII) is a microtubule-associated protein kinase was investigated using a neuronal cell line and bovine brain. Heparin, an inhibitor of CKII, inhibited the phosphorylation of a PC12 cytosolic protein whose molecular weight was similar to that of beta-tubulin. Partially purified PC12 CKII was immunoreactive to an antibody directed against bovine CKII and was able to phosphorylate purified beta-tubulin in a heparin-inhibitable manner when the concentration of tubulin was less than 50 micrograms/ml. To better determine if CKII is a microtubule-associated protein kinase, bovine brain tubulin was chromatographed on FPLC Mono Q and phosphocellulose columns. Several tubulin casein kinase (TCK) activities were apparent. All TCK activities phosphorylated tubulin and casein, but none was able to phosphorylate the CKII-specific synthetic peptide RRREEETEEE. One of these TCK fractions was immunoreactive to the antibody directed against CKII, and this antibody labeled a 50-kDa molecular mass band that had a molecular mass distinctly different from those of the subunits of CKII. Thus, we suggest that a CKII-like protein, but not CKII, might be a microtubule-associated protein.
Crute
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BE
Department of Biological Sciences, State University of New York, Binghamton 13902-6000.
Van Buskirk
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RG
D000595:Amino Acid Sequence; D000818:Animals; D001345:Autoradiography; D001923:Brain Chemistry; D047388:Casein Kinases; D002417:Cattle; D002845:Chromatography; D004591:Electrophoresis, Polyacrylamide Gel; D006493:Heparin / Q000494:pharmacology; D015151:Immunoblotting; D008869:Microtubule-Associated Proteins / Q000032:analysis / Q000502:physiology*; D008969:Molecular Sequence Data; D016716:PC12 Cells; D010766:Phosphorylation; D011494:Protein Kinases / Q000032:analysis / Q000302:isolation & purification / Q000502:physiology*; D051381:Rats; D014404:Tubulin / Q000032:analysis / Q000378:metabolism*
D008869:Microtubule-Associated Proteins; D014404:Tubulin; D006493:Heparin; D011494:Protein Kinases; D047388:Casein Kinases