Characterization of the MTS1^bcrα breakpoint cluster. (A) Restriction map of the MTS1^bcrα region. Only relevant restriction sites are shown. Xb, Xba I; Xh, XhoII; M, Mbo I; E, EcoRI; OL, oligonucleotide. (B) Southern blot analysis of T39p, T117, and T127 rearrangements using the 5′ exon1α probe and Mbo I, XhoII, and Xba I digests. The T39p sample contains approximately 15% nontumoral cells. (C) Reverse view of ethidium bromide–stained gel showing PCR experiments using primers OL17 v OL14 or OL15. Dilutions of DNA from peripheral blood lymphocytes (PBL) from a healthy donor in DNA from the pre-B cell line REH, in which both MTS1 and MTS2 genes are deleted, were included. M, molecular weight marker V (Boehringer Mannheim, Meylan, France); C-, negative control (no DNA). (D) Nucleotide sequence of the MTS1^bcrα breakpoint cluster. Mbo I, Xba I, and EcoRI restriction sites are underlined, and the candidate heptamer targeted by the recombinase activity is boxed. Positions of oligonucleotides used to localize the breakpoints are shown.