A chromosomal translocation (Tx) that interrupts the transcription of either c-Myc or Pvt 1 is the principal lesion in many B cell malignancies including Burkitt's Lymphoma (BL), AIDs-NHL, mouse plasmacytoma (Pct) and possibly multiple myeloma (MM). There is a restriction associated with this Tx such that only the immunoglobulin (Ig) heavy chain gene is found juxtaposed to c-Myc and only the Ig light chain gene is found juxtaposed to Pvt 1. Over the past several years, our laboratory has been instrumental in the elucidation of the structure of the mouse Pvt 1 locus as a means of understanding the relationship between these two divergent Txs which, nevertheless, produce indistinguishable disease phenotypes. In the mouse, we have identified a uniform Pvt1/Ig Ck fusion product which is consistently found in all tumors harboring Pvt 1 associated Txs. We have recently constructed transgenic mice harboring a translocated Pvt 1/Ck segment in order to determine whether 1). these mice produce the Pvt 1/Ck fusion product 2). these mice are immunocompromised and 3). these mice develop tumors of a B cell origin.