Fig. 3.

Top1 protein is decreased by AID expression. (A–C) The protein amounts were measured by Western blot analysis using appropriate antibodies. (A) Wild-type (W) and AID^−/− (A^−/−) splenic B cells were stimulated for the indicated periods by LPS and IL-4. The relative Top1 protein amounts normalized by tubulin are plotted at the right. (B) AID^−/− mouse splenic B cells were infected by retroviruses carrying AIDER (W) or its KSS-mutant (K). 4-OHT (1 μM) was added 24 h after infection. Relative Top1 protein levels at indicated time points after 4-OHT addition are plotted as above. (C) Top1 protein levels in the nucleoplasm fraction of AER cells at indicated time points after 4-OHT addition were measured, normalized by lamin, and are plotted as above.