A DNA-Inducible Kinase Activity Undergoes a Change in Cellular Localization During Development in Arbacia

Prolonged incubation in seawater induces a DNA-dependent protein phosphorylation activity in Arbacia punctulata eggs

Various protein kinases are activated in eggs in response to fertilization. We have previously shown that the induction of DNA-dependent protein phosphorylation activity in the sea urchin eggs is triggered by fertilization. The present study demonstrates that the activation of a DNA-dependent serine/threonine kinase in unfertilized eggs of Arbacia punctulata can be achieved without fertilization. Prolonged incubation in seawater resulted in the activation of the eggs with concomitant induction of DNA-dependent protein phosphorylation activity. The activated eggs when fertilized show a slight increase in the phosphorylation activity 10-min post-insemination. The activity gradually declines as the first and second cleavages proceed. The cytoplasmic extracts of the blastulae, gastrulae, and plutei lack the enzyme activity. These findings reveal that not only fertilization but also egg activation serves as a signal for the induction of a DNA-dependent protein phosphorylation activity in sea urchin eggs suggesting that sperm-entry is not required for the induction of the enzyme activity.

Interaction of Ku protein and DNA-dependent protein kinase catalytic subunit with nucleic acids

The Ku protein-DNA-dependent protein kinase system is one of the major pathways by which cells of higher eukaryotes respond to double-strand DNA breaks. The components of the system are evolutionarily conserved and homologs are known from a number of organisms. The Ku protein component binds directly to DNA ends and may help align them for ligation. Binding of Ku protein to DNA also nucleates formation of an active enzyme complex containing the DNA-dependent protein kinase catalytic subunit (DNA-PKcs). The interaction between Ku protein, DNA-PKcs and nucleic acids has been extensively investigated. This review summarizes the results of these biochemical investigations and relates them to recent molecular genetic studies that reveal highly characteristic repair and recombination defects in mutant cells lacking Ku protein or DNA-PKcs.

DNA-dependent protein phosphorylation activity in Xenopus is coupled to a Ku-like protein

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.