PURIFICATION AND CHARACTERIZATION OF THE DOUBLE-STRANDED DNA-ACTIVATED PROTEIN-KINASE, DNA-PK, FROM HUMAN PLACENTA

The double-stranded DNA-activated protein kinase (DNA-PK) is a serine- threonine protein kinase that is composed of a large catalytic subunit (p350) and a DNA-binding protein of 70 and 80 kDa subunits known as t he Ku autoantigen. When targeted to DNA by free DNA ends, DNA-PK phosp horylates many DNA-binding proteins and transcription factors. previou sly, DNA-PK had only been purified and characterized from transformed human tissue culture cells. Here we report that DNA-PK is an abundant protein in human placenta and lymphocytes. We have purified the placen tal DNA-PK to homogeneity and show that its biochemical properties are similar to those of the HeLa cell enzyme.