Differential inhibition of mammalian DNA polymerases by X-irradiated DNA

Using mammalian DNA polymerases α, β and terminal deoxynucleotidyl transferase, the inhibitory action of X-irradiated DNA on in vitro DNA synthetic activities of these enzymes was examined. It was found that DNA polymerase β was highly sensitive to inhibition by the irradiated DNA as well as DNA polymerase I of E. coli, while DNA polymerase α was at least two hundred times more resistant to inhibition than DNA polymerase β. Terminal deoxynucleotidyl transferase was inhibited moderately by the single-stranded form of the irradiated DNA. Since the inhibition was competitive with respect to a template-initiator for all DNA polymerases or an initiator for terminal deoxynucleotidyl transferase, the differences in sensitivities to the inhibition may be due to the different affinities of the enzymes to the X-ray-induced inhibitory sites on the DNA strand. (author)