The Presence and Expression of RNA Tumor Virus Genes in Normal and Infected Cells: Detection by Molecular Hybridization

Abstract

Three molecular probes have been used to detect genes of the Rous sarcoma virus and mouse mammary tumor virus in normal and infected cells: the 70S ribonucleic acid (RNA) of the viral genomes, and the single- and double-stranded deoxyribonucleic acids (DNA) transcribed from viral RNA by RNA-directed DNA polymerase. The findings indicate that multiple copies of viral genes may be present in the DNA of ostensibly normal cells. However, infection and transformation of mammalian (mouse and rat) cells by Rous sarcoma virus is accompanied by the appearance of virus-specific nucleotide sequences in nuclear DNA of the host cells. The expression of Rous sarcoma virus and mouse mammary tumor virus genes in normal and infected cells has been measured by RNA–DNA hybridization. Virus-specific RNA is present in both normal and transformed cells which produce neither virus nor detectable viral proteins. These data present the possibility that the expression of viral genes is not controlled exclusively by regulation of transcripton.