Pre-steady-state kinetic investigation of bypass of a bulky guanine lesion by human Y-family DNA polymerases.

3-Nitrobenzanthrone (3-NBA), a byproduct of diesel exhaust, is highly present in the environment and poses a significant health risk. Exposure to 3-NBA results in formation of N-(2'-deoxyguanosin-8-yl)-3-aminobenzanthrone (dG(C8-)(N)(-ABA)), a bulky DNA lesion that is of particular importance due to its mutagenic and carcinogenic potential. If not repaired or bypassed during genomic replication, dG(C8-)(N)(-ABA) can stall replication forks, leading to senescence and cell death. Here we used pre-steady-state kinetic methods to determine which of the four human Y-family DNA polymerases (hPolη, hPolκ, hPolι, or hRev1) are able to catalyze translesion synthesis of dG(C8-)(N)(-ABA)in vitro. Our studies demonstrated that hPolη and hPolκ most efficiently bypassed a site-specifically placed dG(C8-)(N-)(ABA) lesion, making them good candidates for catalyzing translesion synthesis (TLS) of this bulky lesion in vivo. Consistently, our publication (Biochemistry 53, 5323-31) in 2014 has shown that small interfering RNA-mediated knockdown of hPolη and hPolκ in HEK293T cells significantly reduces the efficiency of TLS of dG(C8-)(N)(-ABA). In contrast, hPolι and hRev1 were severely stalled by dG(C8-)(N)(-ABA) and their potential role in vivo was discussed. Subsequently, we determined the kinetic parameters for correct and incorrect nucleotide incorporation catalyzed by hPolη at various positions upstream, opposite, and downstream from dG(C8-)(N-)(ABA). Notably, nucleotide incorporation efficiency and fidelity both decreased significantly during dG(C8-)(N)(-ABA) bypass and the subsequent extension step, leading to polymerase pausing and error-prone DNA synthesis by hPolη. Furthermore, hPolη displayed nucleotide concentration-dependent biphasic kinetics at the two polymerase pause sites, suggesting that multiple enzyme•DNA complexes likely exist during nucleotide incorporation.