The c-abl locus is translocated from chromosome 9 to chromosome 22 in chronic myelogenous leukemia (CML), creating the Philadelphia chromosome (22q-, Ph1), one of the most consistent chromosomal abnormalities found in human hematologic malignancy. The K562 cell line is a human cell line originally derived from a patient with CML. We have isolated cloned human c-abl probes to analyze the organization and expression of abl genes in patients with CML and in K562 cells. With these probes, we confirm the amplification of abl genes in K562 cells. In addition, we demonstrate the presence of increased amounts of a novel RNA species hybridizing to a c-abl probe in K562 cells. This same large RNA species is present in addition to two normal transcripts in the leukemic cells of patients with CML. These results provide evidence that the c-abl locus is abnormally expressed in CML.

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