A biochemical approach to the study of the transmission of mouse mammary tumor viruses in mouse strains RIII and C3H.

Mouse mammary tumor virus (MMTV) proviral sequences were detected in the cellular DNA of mammary tumors and livers of RIII and C3H mice by molecular hybridization with radioactively labelled MMTV 60-70S RNA or tritiated MMTV complementary DNA (cDNA). By means of DNA:DNA reassociation kinetics, the DNA of the mammary tumor cells of these two mouse strains were found to contain more MMTV proviral sequences than the DNA of liver cells of these same tumor-bearing mice. Evidence is also presented that the DNA of the liver cells lacks a part (approximately 25%) of the MMTV proviral sequences found in the mammary tumor cells of these mouse strains. The relationship of the extra MMTV proviral sequences found in mammary tumor cells to the early mammary tumor-igenesis seen in these mouse strains is discussed.