LM-PCR analyses of signal ends in RAG1-S723C developing lymphocytes. Three-fold serially diluted linker ligated genomic DNA isolated from sorted (A) DN thymocytes and (B) sorted pro-B bone marrow cells from RAG1^+/+, RAG1^+/S723C, and RAG1^S723C/S723C were used in PCR amplification reactions for detection of signal ends at the indicated loci. PCR amplification of a nonrearranging locus was performed as a normalization control. C indicates non–linker-ligated wild-type genomic DNA. (C) Location of LM-PCR products within the IgH J_H locus. Δ bp indicates number of nucleotides deleted 5′ of the J_H RSS depicted at the top of the columns; triangles, RSSs; and arrows, RAG1/2 cleavage sites. LM-PCR analyses were repeated 3 times on genomic DNA isolated from at least 3 independently sorted DN thymocyte and pro-B-cell samples. Representative results are shown.