The structure and expression of the integrated viral DNA in mouse cells transformed by simian virus 40

Mouse cells stably transformed by simian virus 40 (SV40) contain viral DNA covalently integrated into their chromosomal DNA. We have used molecular cloning techniques to isolate and characterize the integrated viral DNA, together with the flanking cellular sequences, from several lines of transformed cells. We have identified in SV40-infected mouse cells a novel form of viral DNA, which we believe to be the precursor to the integrated DNA. The mRNAs transcribed from the integrated viral DNA templates have been characterized. Integrating the viral genome into the cellular chromosome can significantly alter its transcription pattern and in several cases the altered mRNAs encode novel forms of viral tumour antigen.