Localization of the breakpoints occurring 3′ to MTS1 exon 1β by PCR. (A) Partial map of the region located 3′ to MTS1 exon 1β. The polymorphic dinucleotide CA repeat and the primers OL5 to OL12 used to localize the breakpoints are indicated. Breakpoint-containing regions determined by PCR are represented above by solid bars. (B) Reverse view of an ethidium bromide–stained gel showing representative PCR experiments using primers OL5 v OL7 or OL6. Dilutions of DNA from PBL from a healthy donor in DNA from pre-B cell line REH were included in the experiment. M, molecular weight marker V. One undeleted allele is present in case T84. T128 and T39R could not be studied by PCR, because of the presence of nontumoral cells in the T128 sample and the absence of available material for T39R. (C) Nucleotide sequence of the region located immediately 3′ to MTS1 exon 1β. The position of the relevant oligonucleotides is shown, and candidate heptamers are boxed.