Identification and partial characterization of an endogenous form of mouse mammary tumor virus that is transcribed into the virion-associated RNA genome.

Restriction mapping demonstrated the presence of several distinct proviral forms of mouse mammary tumor virus in the genome of GR mice. One of these proviruses (GR-MTV-2) was highly amplified in GR 3A cells, a cell line derived from a GR mammary tumor. By the criterion of restriction mapping, the amplified GR-MTV-2 provirus found in GR 3A cells was identical to the provirus found in M1.19 cells, a rat cell line infected with virions obtained from GR 3A culture fluid. This result clearly implies that the GR-MTV-2 provirus in GR 3A cells was transcribed into the virion-associated viral RNA genome. Cleavage of either GR 3A or M1.19 cell DNAs with the restriction enzyme Bg1 II gave rise to a 2.6 x 10(6) dalton GR-MTV-2 proviral fragment (ca. 45% of the viral genome). This fragment was isolated and mapped with thirteen restriction enzymes.