The gene product of the BCR-ABL1 fusion gene is a kinase with a higher activity compared to the activity of the native ABL1 kinase. The analysis of the protein structure revealed two responsible mechanisms. First, the cap domain, which covers and blocks the catalytic domain in the native ABL1 protein, is not part of the BCR-ABL1 fusion protein. Second, the fusion protein forms dimers in which the monomers phosphorylate each other, resulting in increased catalytic activity.

BCR-ABL1 and the Philadelphia chromosome – Part 4: Therapy of tumors with BCR-ABL1 fusion proteins
BCR-ABL1 and the Philadelphia chromosome – Part 2: The Philadelphia chromosome
BCR-ABL1 and the Philadelphia chromosome – Part 1: Normal and aberrant karyograms