title: Ectopic restriction of DNA repair reveals that UNG2 excises AID-induced uracils predominantly or exclusively during G1 phase.
abstract: Immunoglobulin (Ig) affinity maturation requires the enzyme AID, which converts cytosines (C) in Ig genes into uracils (U). This alone produces C:G to T:A transition mutations. Processing of U:G base pairs via U N-glycosylase 2 (UNG2) or MutSα generates further point mutations, predominantly at G:C or A:T base pairs, respectively, but it is unclear why processing is mutagenic. We aimed to test whether the cell cycle phase of U processing determines fidelity. Accordingly, we ectopically restricted UNG2 activity in vivo to predefined cell cycle phases by fusing a UNG2 inhibitor peptide to cell cycle-regulated degradation motifs. We found that excision of AID-induced U by UNG2 occurs predominantly during G1 phase, inducing faithful repair, mutagenic processing, and class switching. Surprisingly, UNG2 does not appear to process U:G base pairs at all in Ig genes outside G1 phase.
authors.affiliation: Centenary Institute, the University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: George
authors.initials: G
authors.lastname: Sharbeen
authors.forename: Christine W Y
authors.initials: CW
authors.lastname: Yee
authors.forename: Adrian L
authors.initials: AL
authors.lastname: Smith
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Jolly
mesh_terms: D000818:Animals; D003564:Cytidine Deaminase / Q000378:metabolism*; D045647:DNA Glycosylases / Q000378:metabolism*; D004260:DNA Repair / Q000502:physiology*; D016193:G1 Phase / Q000502:physiology*; D005803:Genes, Immunoglobulin / Q000235:genetics* / Q000502:physiology; D006801:Humans; D017578:Immunoglobulin Class Switching / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D010957:Plasmids / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D059008:Time-Lapse Imaging; D014161:Transduction, Genetic; D014500:Uracil Nucleotides / Q000378:metabolism; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D011993:Recombinant Fusion Proteins; D014500:Uracil Nucleotides; C492570:CCNO protein, human; D045647:DNA Glycosylases; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase