Figure 1.

DMSO rescues stalled Dpo4 primer extension. (a) Chemical structure of the carcinogenic adduct (+)-cis-B[a]P-N ²-dG isomer. (b) Primer extension assay with unmodified template. DNA construct used for the assay is shown on top with 5′-Cy5 labelled primer (Table S1). Primer extension reaction was initiated with 2 nM Dpo4 and aliquots were quenched at the indicated time points before loading onto a denaturing acrylamide gel. The enzyme completes the extension in 30 min both in the absence and presence of DMSO. Both gel panels were taken from the same gel but separated to remove an intervening band. (c) Primer extension assay with B[a]P modified template. Position of the adduct is indicated by red G with an asterisk. Reaction was initiated with 50 nM Dpo4. The adduct stalls Dpo4 one nucleotide before the adduct position (arrow). 10% DMSO rescues stalled Dpo4 after 60 min. Both gel panels were taken from the same gel but separated to remove an intervening band.