Purification and characterization of DNA polymerase alpha of chinese hamster ovary cells

Abstract

The major pol α activity of CHO cells was purified 2 800-fold to near homogeneity and was characterized with respect to its physical and catalytic properties. The purified enzyme, upon analysis in denaturing ‘activity’ gels, displayed a major, 120 kilodalton, catalytically active core and two minor, catalytically inactive components of 180 and 135 kilodaltons. The native form of the enzyme behaved in velocity sedimentation and gel permeation experiments as an asymmetric protein of an apparent Mr. of 515 kilodaltons. The purified enzyme displayed catalytic behavior and inhibitor sensitivity typical of that displayed by other mammalian pol alphas. Specifically, the enzyme: (1) was sensitive to n-ethylmaleimide and the pol α-specific inhibitors, BuPdGTP and aphidicolin; (2) was subject to neutralization by specific monoclonal antibodies raised against human pol α; (3) was devoid of detectable 3′ to 5′ exonuclease activity, and (4) displayed a ribonucleotide-dependent DNA primase activity.