Sixty to seventy per cent of the T(14,18) chromosome translocations which are observed in follicular lymphoma and involve the bcl2 oncogene occur within a short segment of the terminal bcl2 exon designated the mbr (major breakpoint region). All but one of the sequenced breakpoints occur within 100 bp of one another. We have recently shown that 13 of 25 oncogene translocations involving c-myc, bcl1, bcl2 and tcl2 demonstrate, within a few bases of the breakpoints, a 7-for-8 or 8-for-8 match with the chi-like consensus, GC[A/T]GG[A/T]GG (p < 10-10). (chi, GCTGGTGG, is the procaryotic activator of recombination). This association appears to be specific for translocations in which the lymphocyte VDJ recombinase participates. Therefore, we will test the hypothesis that the chi-like sequence, which is also the principal consensus of human minisatellite repeat units, positively influences the probability of a nearby somatic recombination event. Focusing on the mbr region of the bcl2 oncogene, wherein the 5' border is defined by a doublet of the chi-like consensus, we will (1) test the influence of the chi-like consensus alone on VDJ- recombinase-mediated rearrangement of immunoglobulin genes; (2) determine the ability of the entire mbr to affect recombination frequency and product configuration in pre-B cells with an active VDJ recombinase; (3) perform parallel studies on mbr-mediated recombination in an epithelial tumor cell line; (4) conduct a population analysis of a 279 base pair region of the mbr combining a sensitive probe-protection assay with polymerase amplification of genomic DNA to map multiple sequence polymorphisms which we have recently observed in this region. This information will be employed to detect haplotypes representing potential meiotic recombination events and to determine if particular haplotypes are more often associated with t(14,18)-positive follicular lymphoma. The identification, purification and characterization of protein factors mediating recombination through the X consensus will also be pursued. The investigation of sequences which influence translocation of oncogenes may provide important insights into the mechanisms of genetic instability leading to lymphoma. These studies may also uncover additional signal mechanisms involved in immunoglobulin gene rearrangements. Finally, the study of bcl2 translocation site specificity will advance our understanding of the role of potentially recombinogenic signals in increasing the risk of cancer and lymphoma.
