Figure 6.

B cells from mice with reduced levels of APEs have fewer DSBs in Sμ upon CSR induction. LM-PCR was performed on threefold dilutions of DNA isolated from splenic B cells stimulated to undergo CSR for 2 d. Sμ-specific primers were used in conjunction with a linker-specific primer. PCR products were blotted and hybridized to an internal Sμ-specific probe. Input of genomic DNA was normalized by performing PCR for gapdh on the same threefold DNA dilutions. (top) A representative experiment for LPS plus anti–δ-dextran–stimulated B cells. LM-PCR was performed for the 5′ portion of Sμ; the 5′ Sμ primer allows detection of blunt DSBs downstream of this primer. (bottom) A representative experiment for LPS plus IL-4–stimulated B cells. In this experiment, LM-PCR was performed for the 3′ portion of Sμ, detecting blunt breaks upstream of the 3′ Sμ primer. The sizes of the fragments detected on the blots range from 3 to 0.2 kb and, thus, occur over the entire Sμ segment.