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DNA-Dependent Protein Phosphorylation Activity in Xenopus Is Coupled to a Ku-Like Protein

Jyotshnabala Kanungo, Richard S. Cameron, Yoshihiko Takeda and John A. Hardin
Biological Bulletin
Vol. 193, No. 2 (Oct., 1997), pp. 147-152
DOI: 10.2307/1542760
Stable URL: http://www.jstor.org/stable/1542760
Page Count: 6
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DNA-Dependent Protein Phosphorylation Activity in Xenopus Is Coupled to a Ku-Like Protein
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Abstract

DNA-dependent protein kinase (DNA-PK) is a nuclear enzyme and functions as a serine/threonine kinase that has been well characterized in both the human and the mouse. The regulatory subunit of DNA-PK is the Ku autoantigen. To demonstrate that a Ku-like protein is present in Xenopus oocytes, we used immunoprecipitation analysis with a monoclonal antibody raised against human Ku antigen and autoimmune serum containing anti-Ku antibodies. Metabolic labeling studies indicate that the Ku-like protein is synthesized mainly in late vitellogenic oocytes. By using a specific peptide substrate for DNA-PK, we demonstrate the activity of a DNA-dependent protein kinase in oocyte extracts. The kinase activity requires the Ku-like protein, since extracts depleted of Ku protein by immunoadsorption with human anti-Ku antibodies fail to demonstrate the DNA-dependent phosphorylation activity. The increased enzyme activity in vitellogenic oocytes may be correlated to the increased levels of Ku protein observed in these oocytes compared to the pre- and early vitellogenic oocytes.

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