Anti-Flag IPs were performed on whole cell extracts from retrovirally transduced pro-B cells expressing constructs of interest: FNT tag, FNT-tagged core Rag2, C terminus of Rag2, R2FL, or full-length T-B-SCID/OS Rag2 mutants. Western immunoblotting analysis is shown for Rag2 and acetylated Histone H3 (AcH3). Flag IP loading was analyzed by Western blotting for β-actin on 1:1,000 input volume.