Viral integration near c-myc in 10-20% of mcf 247-induced AKR lymphomas

We induced AKR thymomas by injecting retrovirus MCF 247 that we had tagged with a fragment of phage lambda in its U3 region. About 10-20% of the 26 primary tumors studied showed both rearranged and germline c-myc bands in Southern blots. The rearranged c-myc genes were cloned from two of the tumors and studied by Southern analysis in two others. In all four cases, rearrangement was due to integration of MCF 247 proviruses about 2 kilobases (kb) 5' of the three c-myc exons and in the opposite transcriptional orientation. Thus, viral integrations were clustered within a 1-kb range in the tumors that revealed c-myc rearrangements. Three of the four proviruses appeared to be intact, whereas the fourth had an internal deletion of about 3 kb.