Molecular cloning of the breakpoint of t(11;22) (q23;q11) chromosome translocation in an adult acute myelomonocytic leukaemia.

Southern blot analysis with a cDNA probe of MLL indicated that the breakpoint is in a BamHI 8.3 kb fragment which carries the exon 5-11 of MLL gene in DNA from an adult acute myelomonocytic leukaemia with a t(11;22) (q23;q11) translocation. The structural analysis of the rearranged MLL locus demonstrated that the breakpoint is localized between exon 8 and 9 of MLL locus. The normal counterpart fused to the MLL locus was proved to be derived from chromosome 22q11(AF-22) by somatic cell hybrids analysis and FISH. By FISH, AF-22 was localized to the region more centromeric to the BCR gene.