Phenylalanine 171 is a molecular brake for translesion synthesis across benzo[a]pyrene-guanine adducts by human DNA polymerase kappa.

Human cells possess multiple specialized DNA polymerases (Pols) that bypass a variety of DNA lesions which otherwise would block chromosome replication. Human polymerase kappa (Pol kappa) bypasses benzo[a]pyrene diolepoxide-N(2)-deoxyguanine (BPDE-N(2)-dG) DNA adducts in an almost error-free manner. To better understand the relationship between the structural features in the active site and lesion bypass by Pol kappa, we mutated codons corresponding to amino acids appearing close to the adducts in the active site, and compared bypass efficiencies. Remarkably, the substitution of alanine for phenylalanine 171 (F171), an amino acid conserved between Pol kappa and its bacterial counterpart Escherichia coli DinB, enhanced the efficiencies of dCMP incorporation opposite (-)- and (+)-trans-anti-BPDE-N(2)-dG 18-fold. This substitution affected neither the fidelity of TLS nor the efficiency of dCMP incorporation opposite normal guanine. This amino acid change also enhanced the binding affinity of Pol kappa to template/primer DNA containing (-)-trans-anti-BPDE-N(2)-dG. These results suggest that F171 functions as a molecular brake for TLS across BPDE-N(2)-dG by Pol kappa and that the F171A derivative of Pol kappa bypasses these DNA lesions more actively than does the wild-type enzyme.