Mammary Tumour Virus Specific Nucleotide Sequences in Mouse DNA

Abstract

IN most mouse strains with a high incidence of mammary tumours, mouse mammary tumour virus (MTV) is transmitted only in the milk^1,2, but in GR mice it is also transmitted by the gametes of both sexes in a simple autosomal dominant pattern^2,3. Since inheritance of an MTV susceptibility gene cannot be shown to explain these observations², either there are MTV genes in GR but not in low incidence strains or the mice inherit factors governing the expression of such genes³. In the latter case, both types would contain virus-specific genes, but only the GR mice would consistently express them. To choose between these alternatives, we have measured MTV-specific nucleotide sequences in DNA from high and low tumour incidence mouse strains⁴. Unlabelled cellular DNA was tested for virus-specific sequences by its capacity to accelerate the reassociation of labelled double stranded DNA transcribed in vitro by the MTV virion reverse transcriptase. DNA from both GR (MTV +) and C57BL/6 (MTV−) strains accelerates the reannealing of the labelled polymerase product, causing an apparent reduction in the C₀t_½ values consistent with the presence of sixty to a hundred copies of those sequences in both strains.