Fig. 2.

Inefficient extension of slipped DNA substrates leads to an opportunity for DnaQ to realign the primer-template junction. (A) In vitro primer extension analysis indicates that DinB(Y79L) (open circles) is modestly less efficient at extending T-4 substrates than DinB (closed circles), but the two polymerases are indistinguishable at extending a nonslipped control [DinB, closed triangles; DinB(Y79L), open triangles]. (B) Plot of the mutation frequency measured by the CC108 lac mutant reversion assay for strains overexpressing DinB (pGY782) or DinB(Y79L) (pGY782 Y79L) compared to that for a vector control (pWSK30). (C) Overexpression of DinB(Y79L) in CC108 ΔdnaQ::kan results in an increase in mutation frequency comparable to that of DinB overexpression. The mutation frequency and standard deviation reported is derived from 3 independent CC108 ΔdnaQ::kan isolates, which were freshly transformed with DinB-overexpressing plasmids. (D) Expression of DnaQ from a multicopy plasmid (pPF2) decreases the mutation frequency of a strain overexpressing DinB (pGY782).