PCR amplification of endogenous rearrangements in RAG1-S723C homozygous developing lymphocytes. (A) TCRβ rearrangements. Genomic DNA from purified DN thymocytes from RAG1^+/+ (WT) and RAG1^S723C/S723C (S723C) mice and a nonrearranging tissue (tail) was PCR amplified to detect Dβ1 to Jβ1 and Dβ2 to Jβ2 rearrangements. For Dβ1 to Jβ1 rearrangements, genomic DNA was first digested with the XbaI restriction endonuclease. Control PCR amplification of a nonrearranging locus was performed to normalize levels of input DNA. Rearrangements were detected by Southern blot hybridization using an oligonucleotide probe. Experiments (A-C) were repeated 3 times with genomic DNA samples from 3 different sets of mice; representative results are shown. (B) IgH rearrangements. Genomic DNA from sorted pro- and pre-B-cell populations from RAG1^+/+ (WT) and RAG1^S723C/S723C (S723C) mice and a nonrearranging tissue (kidney) was PCR amplified to detect D_H to J_H rearrangements. (C) Endogenous TCRδ signal joints. Levels of extrachromosomal signal joints formed between TCR Dδ2 and Jδ1 RSSs were detected by PCR amplification of genomic thymocyte DNA isolated from RAG^+/+ (WT) and RAG1^S723C/S723C (S723C) mice and a nonrearranging tissue (tail). Vertical lines have been inserted to indicate repositioned gel lanes.