Human DNA polymerase ι promotes replication through a ring-closed minor-groove adduct that adopts a syn conformation in DNA

Acrolein, an α,β-unsaturated aldehyde, is generated in vivo as the end product of lipid peroxidation and from oxidation of polyamines. The reaction of acrolein with the N² group of guanine in DNA leads to the formation of a cyclic adduct, γ-hydroxy-1,N²-propano-2′- deoxyguanosine (γ-HOPdG). Previously, we have shown that proficient replication through the γ-HOPdG adduct can be mediated by the sequential action of human DNA polymerases (Pols) ι and κ, in which Polι incorporates either pyrimidine opposite γ-HOPdG, but Polκ extends only from the cytosine. Since γ-HOPdG can adopt either a ring-closed cyclic form or a ring-opened form in DNA, to better understand the mechanisms that Pols ι and κ employ to promote replication through this lesion, we have examined the ability of these polymerases to replicate through the structural analogs of γ-HOPdG that are permanently either ring closed or ring opened. Our studies with these model adducts show that whereas the ring-opened form of γHOPdG is not inhibitory to synthesis by human Pols η, ι, or κ, only Polι is able to incorporate nucleotides opposite the ring-closed form, which is known to adopt a syn conformation in DNA. From these studies, we infer that (i) Pols η, ι, and κ have the ability to proficiently replicate through minor-groove DNA lesions that do not perturb the Watson-Crick hydrogen bonding of the template base with the incoming nucleotide, and (ii) Polι can accommodate a minor-groove-adducted template purine which adopts a syn conformation in DNA and forms a Hoogsteen base pair with the incoming nucleotide.