Variant (6;15) translocations in murine plasmacytomas involve a chromosome 15 locus at least 72 kb from the c-myc oncogene.

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Abstract
The variant (6;15) translocations in murine plasmacytomas join the myc oncogene‐bearing band of chromosome 15 and the immunoglobulin kappa band of chromosome 6. We recently cloned a region from chromosome 15 linked to C kappa and have now used probes from that region to define the major locus of plasmacytoma variant translocations, which we denote pvt‐1. In five of nine plasmacytomas we analysed, the 6;15 translocation resulted from reciprocal recombination between the C kappa locus and a 4.5‐kb region of pvt‐1. Moreover, nearby we located the region shown by others to have undergone a complex (15;12;6) translocation in plasmacytoma PC7183. All the chromosome 6 breakpoints fell between 1 and 3 kb 5′ to C kappa but only two were near J kappa genes. Thus the J kappa ‐C kappa region appears to be a recombination ‘hot spot’ in lymphocytes, but the breaks are unlikely to be mediated via V/J recombination enzymes. Comparison of a cloned 108‐kb region across pvt‐1 and another of 52 kb across c‐myc established that the pvt‐1 breakpoints lie at least 72 kb from the c‐myc promoters. Since c‐myc is expressed at a substantial level, the 6;15 translocation apparently activates c‐myc. Activation may occur directly, at a remarkable distance along the chromosome, or indirectly, via a putative pvt‐1 gene product.