UASt regulatory sequences drive expression of a Hsap\ABL1::Hsap\BCR fusion gene that produces a p210 kDa protein. This particular gene fusion accounts for over 95% of chronic myeloid leukemia patients. In addition, the protein carries a T to I amino acid replacement at position 315 in the Hsap\ABL1 kinase domain, a point mutation that results in resistance of tumors to many tyrosine kinase inhibitors.