MOLECULAR CHARACTERIZATION OF A VARIANT PH(1) TRANSLOCATION T(92211) (Q34Q11Q13) IN CHRONIC MYELOGENOUS LEUKEMIA (CML) REVEALS THE TRANSLOCATION OF THE 3'-PART OF BCR GENE TO THE CHROMOSOME BAND 11Q13

We performed cloning and sequence analysis of translocation junctions at 11q- and 22q- (Ph(1)) chromosomes and the corresponding germline DN As of a variant Ph(1)-positive CML with t(9;22;11)(q34;q11;q13). South ern blot analysis using probes for different regions of bcr mapped the translocation break near the 5'-side of bcr exon 4. Cloning, Southern blot analysis and restriction map analysis of both bcr fragments show ed that the part of bcr 3'- to the translocation break moved to 11q13. Sequence analysis of the translocation junction on the Ph(1) chromoso me showed that the translocation break occurred 63 bp upstream of exon 4. Compared to the germline sequence, bcr sequence from the transloca ted partners showed deletion of seven basepairs at the site of translo cation. A probe derived from the 5'-region of the clone isolated from the 11q- chromosome identified clonal rearrangements in the leukemic D NA. Restriction map and sequence analysis showed that this clone consi sted of the 3'-half of the glutathione S-transferase Pi (GST-Pi) gene and the 3'-part of bcr. We identified two point mutations in the GST-P i allele involved in translocation. Northern blot analysis showed that the GST-Pi gene was expressed in the leukemic cells at blast crisis b ut not at chronic phase; however, no fusion mRNA between GST-Pi and bc r was identified. We did not find any sequence homology between 11q13 DNA and 22q11 DNA around the translocation breakpoints; however, seque nces homologous to ALU repeats were identified close to the sites of t ranslocation breaks at 22q11 and 11q13. This study supports our hypoth esis that variant Ph(1) translocations may occur as primary cytogeneti c changes similar to the classical Ph(1) translocations.