Given the task definition and input, reply with output. Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.

Chronic myeloid leukaemia (CML) is characterised by the occurrence of the Philadelphia (Ph) chromosome (9/22 translocation) and the formation of a fusion protein--the BCR-ABL transcript with constitutive activation of the BCR-ABL tyrosine kinase and consequent changes in the intracellular signal transduction, which is responsible for the deregulated myeloid cell proliferation. STI571 (signal transduction inhibition number 571) is a potent and selective inhibitor of the BCR-ABL tyrosine kinase. In the chronic phase of the disease, normal peripheral blood values are achieved within the first month of treatment in the large majority of patients and in many patients also a cytogenic response within the following months. The results in the advanced phase are far less favourable, which is explained by the development of resistance owing to reactivation of the BCR-ABL signal transduction. Side effects are primarily nausea, vomiting, various rashes, oedema, most often in the periorbital region, and musculoskeletal symptoms, including muscle cramps. Perspectives for treatment with STI571 are described, as are combinations with alpha-interferon and other cytostatics with a synergistic profile.
What tyrosine kinase, involved in a Philadelphia- chromosome positive chronic myelogenous leukemia, is the target of Imatinib (Gleevec)?