Detection of Ig/c-myc recombinations in different regions of the intestine in two BALB/cAn mice. The gut was sectioned into 10 fragments and the DNA preparations were analyzed by duplicate PCR amplifications and electrophoresed on 2% agarose gels. The presence of Ig/c-myc recombinations are indicated by arrows. The upper gel shows samples from a mouse 7 days after pristane treatment; identical products were obtained in lanes 01 (duodenum), 08 (proximal ileum), and 11 (middle ileum) and in 13, 14 (middle ileum), and 18 (distal ileum) indicating a common origin of these cells. In the second, untreated mouse (lower gel), clones from distal (lanes 35 and 36) and terminal ileum (lane 38) are related by virtue of their identical Igμ/c-myc recombination sequence. The upper sequence shows 24 bp of switchα (GenBank “MUSIALPHA” #2293-2270) followed by switchμ (“MUSIGCD07” #5550-5529) and c-myc. In the lower recombination, the same 18 bp of switchμ is preceded by a sequence that has a switchμ-typical pattern of pentamers, but that could not be aligned to germline. It originates most likely from the part of switchμ that has not yet been sequenced. The two recombinations indicate that the Igμ/c-myc rearrangement was followed by additional recombinations.