Gradual decline of mutations 3’ of VDJH also in AID-transgenic mice. A, Occurrence of cytidine in the 1.1 kb region at the start of the Ig heavy chain JC intron. The bars are Cs on both DNA strands. B, Positions of WRC hotspots in both DNA strands. C, Mutation pattern in the AID-trangenic, AID+/+ mice. D, Mutation pattern in the AID-transgenic, AID−/− mice. E, The Ig heavy chain gene (not to scale). Bent arrow, transcription initiation site; variable region (VDJ), JC intron (the line between VDJ and C), and constant region (C) are indicated. The sequenced region extends from 1 to 1,100 bp of the JC intron.