Rev1 Recruits Ung to Switch Regions and Enhances dU Glycosylation for Immunoglobulin Class Switch DNA Recombination

By diversifying the biological effector functions of antibodies, class switch DNA recombination (CSR) plays a critical role in the maturation of the immune response. It is initiated by activation-induced cytidine deaminase (AID)-mediated deoxycytosine deamination, yielding deoxyuridine (dU), and dU glycosylation by uracil DNA glycosylase (Ung) in antibody switch (S) region DNA. Here we showed that the translesion DNA synthesis polymerase Rev1 directly interacted with Ung and targeted in an AID-dependent and Ung-independent fashion the S regions undergoing CSR. Rev1^-/- Ung^+/+ B cells reduced Ung recruitment to S regions, DNA-dU glycosylation, and CSR. Together with an S region spectrum of mutations similar to that of Rev1^+/+ Ung^-/- B cells, this suggests that Rev1 operates in the same pathway as Ung, as emphasized by further decreased CSR in Rev1^-/- Msh2^-/- B cells. Rescue of CSR in Rev1^-/- B cells by a catalytically inactive Rev1 mutant shows that the important role of Rev1 in CSR is mediated by Rev1@s scaffolding function, not its enzymatic function.