The ABL-BCR fusion gene is expressed in chronic myeloid leukemia..     ///    By reverse transcription/polymerase chain reaction amplification (RT/PCR) we have detected ABL-BCR mRNA in cells from 31 of 44 BCR-ABL positive CML patients and 3 of 5 CML cell lines.     ///    "In 2 patients, the BCR exon b3 was not present in either the BCR-ABL or the corresponding ABL-BCR transcript, whereas in 5 patients exon b3 was present in both transcripts. "    ///    "The ABL-BCR transcripts encoded one or, more rarely, both of the two potential junctions, designated ABL-b3 and ABL-b4, which differed in size by 75 bp. "    ///    "If an ABL-BCR gene product is produced in CML cells, it may be relevant as a mechanism for deregulating the GTPase activating protein (GAP) function of BCR.. "    ///    ABL-BCR expression consisted of ABL(Ib)-BCR mRNA in 26 patients and of both ABL(Ib)-BCR and ABL(Ia)-BCR mRNA species in 6 patients.     ///    "Direct sequencing of PCR fragments representing the full-length coding sequence of ABL-BCR cDNAs type Ib-b3, Ia-b3, Ib-b4, and Ia-b4 showed an open reading frame predicted to encode fusion proteins of 370 to 414 amino-acids. "    ///    " Although the BCR-ABL hybrid gene on chromosome 22q-plays a pivotal role in the pathogenesis of chronic myeloid leukemia (CML), little is known of the reciprocal chimeric gene, ABL-BCR, formed on chromosome 9q+. "