Aphidicolin-resistant and -sensitive base excision repair in wild-type and DNA polymerase $beta;-defective mouse cells

Abstract

Several DNA polymerases (Pols) can add complementary bases at the gap created during the base excision repair (BER). To characterize the BER resynthesis step, the repair of a single abasic site by wild-type and Pol β-defective mouse cell extracts was analysed in the presence of aphidicolin, a specific inhibitor of replicative Pols. We show that there is a competition between distributive and processive Pols for the nucleotide addition at the primer terminus. In wild-type cell extracts, the initial nucleotide insertion involves mainly Pol β but the elongation step is carried out by a replicative Pol. Conversely, in Pol β-null cell extracts the synthesis step is carried out by a replicative Pol without any switching to an auxiliary polymerase. We present evidence that short-patch repair synthesis occurs even in the absence of both Pol β and replicative Pols. Exogeneously added purified human Pol λ was unable to stimulate this back-up synthesis.