DNA polymerase kappa is the primary translesion synthesis polymerase for aldehyde ICLs.

DNA interstrand crosslinks (ICLs) are highly cytotoxic lesions that block essential cellular processes like replication and transcription. Endogenous ICLs can be induced by reactive aldehydes produced during normal cellular metabolism. Defective repair of these aldehyde-induced ICLs is associated with Fanconi anaemia (FA), a cancer predisposition syndrome. We previously showed that acetaldehyde-induced ICLs are repaired by the FA pathway and a novel excision-independent pathway. Here, we demonstrate that ICLs induced by acrolein, another cellular aldehyde, are also repaired by both pathways, establishing the generality of aldehyde ICL repair. Focusing on the FA pathway, we identify DNA polymerase kappa (Polκ) as the primary translesion synthesis (TLS) polymerase responsible for the insertion step during lesion bypass of unhooked aldehyde ICLs. This function requires Polκ's catalytic activity and PCNA interaction domains but is independent of Rev1 interaction. In contrast, Polκ has a non-catalytic role in the extension step of cisplatin ICL repair that is dependent on Rev1 interaction. Our work reveals a key role for Polκ in aldehyde ICL repair and provides mechanistic insights into how different ICL structures determine the choice of TLS polymerases during repair.