Viral DNA integration patterns of primary SV40 tumors.

Primary tumors were induced in newborn Syrian hamsters by Simian virus 40 (SV40). These tumors were subjected to restriction enzyme analysis and each was found to have a unique viral integration pattern. One primary tumor was able to produce tumor foci in the lungs. Transplantation of this tumor resulted in a simplification of the integration pattern. The primary tumor was then cloned, revealing a heterogeneous population. When the cloned populations were transplanted subcutaneously into adult animals, restriction enzyme analysis of the tumors revealed no rearrangement of the viral DNA in either subcutaneous tumor or lung foci. Tumor cells isolated from the lungs were transplanted subcutaneously in adult animals and restriction enzyme analysis revealed an increase of free viral DNA and new sites of viral integration.