The Mode of Inhibitory Action by Aphidicolin on Eukaryotic DNA Polymerase α

Abstract

The mode of action by aphidicolin on DNA polymerase α from the nuclear fraction of seaurchin blastulae was studied. The inhibition of DNA polymerase α by aphidicolin was uncompetitive with activated DNA and competitive with the four deoxynucleoside triphosphates using activated DNA as a template-primer. For truncated (residual or limited) DNA synthesis with only three deoxynucleoside triphosphates, aphidicolin inhibited the residual synthesis more strongly in the absence of dCTP than in the absence of each of the other three deoxynucleoside triphosphates. The inhibition was reversed with excess dCTP but not with the other three deoxynucleoside triphosphates. That is, aphidicolin inhibited DNA polymerase α by competing with dCTP with a K_i value of 0.5 μg/ml and by not competing with the other three deoxynucleoside triphosphates. dTMP incorporation with the activated DNA was more sensitive to aphidicolin than dGMP or dTMP incorporation with poly(dC) · (dG)_12–18 or poly(dA) · (dT)_12–18. Similar results were obtained for DNA polymerase α (B form) from mouse myeloma MOPC 104E.