Effect of X Irradiation on the Priming Activity of Dna

The activity of DNA as a primer for RNA- and DNApolymerase from E. coli was severely depressed by x irradiation in doses of 1000 r or less. The priming activity for DNA-polymerase appeared to be more readily affected and was reduced in the case of DNA extracted from irradiated lymphoblasts, as well as for DNA irradiated in dilute solution. The optimum concentration of primer in the DNApolymerase reaction was lower for irradiated DNA than for control DNA, concentrations higher than the optimum being inhibitory in both cases. Mixtures of irradiated and control DNA showed a lower priming activity than that found for the control DNA alone, the extent of the decrease depending on the ratio of the concentration of the control to the irradiated DNA in the mixture, as well as on the amount of enzyme present. (P.C.H.)