Rearrangement of a DNA sequence homologous to a cell-virus junction fragment in several Moloney murine leukemia virus- induced rat thymomas (T-cell lymphoma/provirus/specific integration site)

We have studied the integrated proviruses in Moloney murine leukemia virus-induced rat thymomas. By Southern blot analysis, we found several complete integrated proviruses in each tumor. In most tumors, we could not detect defective or recombinant proviruses. Several of these integrat- ed proviruses (with their flanking cellular sequences) from a single tumor were cloned in Charon 4A. Their flanking cellu- lar fragments were subcloned into pBR322 and used as a probe to screen other thymoma DNAs. With one clone (pMo-1C) used as a probe, we could detect novel fragments in 11 out of 20 thymoma DNAs analyzed. In three of these thymomas we could analyze in more detail, it appears that these novel frag- ments are generated by the insertion of a provirus. This specif- ic integration of Moloney provirus in the host genome may represent an important genetic event leading to tumor forma- tion.