Inhibition of DNA polymerases alpha and gamma by rifamycin derivative AF/013

The nature of the inhibitory effects of rifamycin derivative AF/013 (O-n-octyloxime of rifamycin SV) on DNA polymerases alpha and gamma were studied. Lineweaver-Burk analysis of the inhibition of DNA polymerases with respect to a substrate and template-primer showed a different mode of inhibition by AF/013 for each: the inhibition of DNA polymerase gamma was competitive with both dTTP and poly(rA)-oligo(dT), while that of DNA polymerase alpha was competitive with activated calf thymus DNA and non-competitive with dTTP. Further analysis of the competitive mode of the inhibition of DNA polymerase alpha, using poly(dT)-oligo(rA) as a template-primer, demonstrated that the primer molecule competed with AF/013. A change of effective divalent metal ion (Mn2+ in place of Mg2+) in the reaction mixture did not alter this competitive mode of inhibition with respect to the template-primer. The results of experiments to obtain further insight into the mechanism of drug-enzyme interaction suggest that AF/013 binds tightly to DNA polymerase alpha, and inhibits the process of chain elongation with DNA polymerases alpha and gamma.