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. 2016 May;101(5):541–558. doi: 10.3324/haematol.2015.139337

Figure 4.

Figure 4.

The structure of the normal BCR and ABL1 genes and the fusion transcripts found in Ph-positive leukemias. The ABL1 gene contains two alternative 5′ exons (named 1b and 1a) followed by 10 ‘common’ exons numbered a2–a11 (green boxes). Breakpoints in CML and Ph-positive ALL usually occur in the introns between exons 1b and 1a or between exons 1a and a2 (as shown by vertical arrows). The BCR gene comprises a total of 23 exons, 11 exons upstream of the M-BCR region, five exons in the M-BCR that were originally termed b1–b5 and now renamed e12–e16, and seven exons downstream of M-BCR (orange boxes). For convenience, only exons e1, e12–e16 and e23 are shown. Breakpoints in CML usually occur between exons e13 (b2) and e14 (b3) or between exons e14 (b3) and e15 (b4) of the M-BCR (as shown by two vertical arrows placed centrally). The majority of patients with Ph-positive ALL have breakpoints in the first intron of the gene, between e1 and e2 (arrow at left). Three possible BCR–ABL1 mRNA transcripts are shown below. The first two (e13a2 and e14a2, respectively) are characteristic of CML. The bottom mRNA (e1a2) is found in the majority of patients with Ph-positive ALL.