Cloning and sequencing of viral integration site in human fibroblasts immortalized by simian virus 40

We have analyzed cellular DNA sequences at the viral genome integration site in a human fibroblast cell line VA13 immortalized by simian virus 40 (SV40). The computer analysis of the junctional cellular DNA sequences did not show any homology to the DNA sequences previously reported. This suggests that immortalization by SV40 was not induced by the destruction of any known oncogene or anti-oncogene at the integration site. We did not find the precise substantial sequence homology at the junctional site between the cellular DNA and SV40 DNA, indicating that the recombination mechanism involved does not require precise sequence homology and therefore, SV40 genome was probably not integrated by homologous recombination. Short direct and inverted repeats of 5 to 29 nucleotides were found in the junctional cellular and SV40 DNA. Cellular DNA abutting SV40 DNA was found by the Northern blot analysis to be expressed in diploid human fibroblasts and SV40-transformed cells. The nature of this RNA is now under study.