Fig. 1.

APE1's endonuclease activity is essential for CSR. (A) Schematic representation of the various APE1 mutants used in the CSR complementation experiments. (B) Representative IgA population of Ape1-null CH12F3-2A cells after transient introduction of various APE1 constructs. Data are represented as mean ± SD. (C) IgA switching efficiency of Ape1-null CH12F3-2A cells stably expressing the empty vector, WT, or Y170F mutant of APE1. APE1 protein expression was determined by Western blot (Upper), and CSR efficiency was measured by FACS as the percentage of cell surface IgA expression at indicated time after CIT stimulation (Lower). Data are represented as mean ± SD. (D) Representative flow cytometry (FACS) profile of the IgA switching population under CIT (−) and (+) conditions.