Characterization of the MTS1^bcrβ cluster and cloning of 3 representative rearrangements. (A) Partial map of the DNA region flanked by STS2.3 and STS2.7. Localization of the 2 breakpoints occurring 5′ to MTS1 exon 1β (T73 and T79) and of the 14 breakpoints occurring 3′ to exon 1β is shown. Breakpoints were localized by Southern blot experiments using the MTS1 exon 1β probe and BglII digests, and in certain cases, Sal I, BamHI, EcoRI, and HindIII digests. Bracketed cases show rearranged fragments of identical length in various digests. (B) Top: Schematic representation of MOLT4, T42, and T123 rearrangements. Vertical arrows represent breakpoints. Insert: Hybridization with junction-specific oligonucleotides after direct PCR amplification of the MOLT4 breakpoint using primers OL5 and OL22 and the T42 and T123 breakpoints using primers OL5 and OL20. PCR products were successively hybridized with ³²P-radiolabeled oligonucleotides specific for junctional sequences of MOLT4 (AJ MOLT4), T42 (AJ T42), and T123 (AJ T123) and with a common internal oligoprobe, OL6. Bottom: Nucleotide sequence alignment of MOLT4, T42, and T123 rearrangements with chromosome 9 germline sequences. Heptamers are boxed, and putative N regions are underlined. No definite nonamer was found.