Is dna dependent protein kinase, dna-pk, a dual function (phospholipid/protein) kinase?
Phosphorylation of macromolecules such as proteins and lipids regulates diverse cellular processes, including DNA repair and the cell cycle. Until recently, lipid and protein kinase activities were considered to be separate biochemical entities. However several laboratories have reported potential "dual function" kinases. DNA-activated protein kinase is a serine/threonine protein kinase that interacts with a DNA end-binding heterodimeric protein, Ku activated by double-stranded DNA. Genomic clones that contain the DNA-PK gene complement the murine scid defect, indicating that DNA-PK affects double-strand (ds) break repair and V(D)J recombination. Here we describe the cDNA sequence of the region that corresponds to about 100 kDa of C-terminal sequence of this large protein. This region contains a kinase domain that has strong homology to phosphatidylinositol kinases. We also find PI-4 kinase activity in some highly purified preparations of DNA-PKcs, although this is not always the case. Cryptic PI-4 kinase activity of DNA-PK could be revealed either by post translational modification of the DNA-PKcs, for example by phosphorylation or partial proteolysis of DNA-PKcs, or by association with regulatory protein(s). Fractionation of HeLa nuclear extract on sequence specific DNA affinity column reveals three major polypeptides in addition to DNA-PKcs. in fractions with peak protein kinase activity. None of these polypeptides are Ku-related. Further analysis of these proteins involving their possible role in the regulation of DNA-PKcs is underway.
Malik, N; Poltoratsky, VP; York, JD; Lieber, MR; Carter, TH
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