AID-induced deamination at antibody switch region is restricted to early G1. (A and B) Prolonged staying in M phase upon nocodazole release does not significantly increase the level of AID-induced mutations. (A) Cell cycle distribution of In vitro–cultured B lymphocytes at different time points upon nocodazole release. Cells in M, cytokinesis, and G1 are resolved by combining DNA fluorescence peak (DAPI-H) and intensity (DAPI-A; Gasnereau et al., 2007). Insets show DAPI-A profiles only. Nocodazole-treated cells were collected at 0, 1, and 2 h after release. In red are the sorted cell populations analyzed in Fig. 3 B. (B) Mutation rates at 5′-Sμ, as determined by MutPE-Seq. Red, blue, and gray represent C-to-T, G-to-A, and all other mutations, respectively. n.s., nonsignificant, one-tailed bootstrap test. One experiment is shown. (C) Nocodazole-treated cells were collected at 0, 1, and 5 h after release for mutational analysis with Pfu-Cx. Red, the sorted cell populations analyzed in D and E. (D and E) Mutation frequencies at 5′-Sμ are shown as a histogram (D) or at single-nucleotide resolution (E). The numbers in the rectangles indicate the overall mutation rate. Red, blue, and black represent C-to-T, G-to-A, and all other mutations, respectively. n.s., nonsignificant; **, P < 0.01, one-tailed bootstrap test. Two independent experiments were performed.