Sequence-specific DNA-binding proteins within the Mbcr on the Ph1 chromosome

Characterization of genomic BCR-ABL breakpoints in chronic myeloid leukaemia by PCR

In order to understand better the mechanism of translocation between the BCR and ABL genes in CML, we have exploited a 'bubble PCR' technique to clone genomic breakpoints. BCR-ABL junction fragments were successfully amplified and sequenced in 14/32 (43%) patients tested. Breakpoints were dispersed throughout the major breakpoint cluster region without any clustering or hot spots. In three cases Alu sequences were found at or near the breakpoint on the ABL side of the translocation but no other obvious sequence homologies were found either in BCR or ABL. The translocation event was characterized further in three other patients by amplifying the reciprocal ABL-BCR junction on the 9q+ chromosome and also normal ABL around breakpoints. In two of these patients a few nucleotides of BCR and ABL were either duplicated or deleted on translocation, suggesting that staggered cuts had been made in the DNA strand prior to recombination. In the third patient 50 bp of ABL was deleted and 159 bp of M-BCR including exon b3 was duplicated, indicating either that the single-stranded cuts may span a larger distance than previously thought or that another mechanism, perhaps involving gene conversion, may be involved in this instance.

Influence of M-BCR breakpoint sites on the duration of chronic phase in 100 patients with chronic myelocytic leukemia

Rearrangements of the bcr (M-BCR) gene were studied in 100 patients with chronic myelocytic leukemia (CML). To determine the significance of a chimeric gene expression in the progression of CML, we analyzed 43 patients for bcr-ABL chimeric mRNA expression. Both DNA and RNA analyses revealed a possible influence of breakpoint sites in the bcr region on the duration of the chronic phase. Patients with the breakpoint located at about the 1-kb region between BamHI and HindIII in bcr exon 3 (region C2) had a significantly shorter chronic phase (31 months) (p = 0.028) than patients in whom the breakpoint was located in other regions. When the bcr locus was divided into 5' and 3' regions as for the BamHI cleavage site located near the 5' region of bcr exon 3, the chronic phase duration in patients with the 5' site (HindIII-BamHI) and 3' site (BamHI-EcoRI site) was 75 and 38 months, respectively. However, the difference was not statistically significant (p = 0.128). These results suggest that only the breakpoint site at C2 on the bcr locus, rather than breakpoint sites in other regions, has an important role in the progression of CML.