Reconstituted DNA lagging strand maturation and BER were performed to determine the effects of pol β bypass of a cdA on completion of DNA lagging strand maturation and BER. Substrates containing a 5′-phosphate or 5′-THF residue with a 1-nt gap opposite a template 5′R-cdA or 5′S-cdA were incubated with indicated BER enzymes at the experimental conditions described in Materials and Methods. Lanes 1, 5, 9 and 13 represent substrates only. Lanes 2–4, 6–8, 10–12 and 14–16 correspond to reconstitution reaction mixtures with 10 nM FEN1 and 5 nM LIG I in the presence of 5, 10 and 25 nM pol β, respectively. Substrates were 32P-labeled at the 5′-end of the upstream primer as indicated. Substrates are illustrated schematically above the gel.