Independent Segregation of Loci for Activation of Biologically Distinguishable RNA C-Type Viruses in Mouse Cells

Two genetic loci for induction of RNA C-type virus in BALB/c mouse embryo cells segregate independently in backcross embryo cell lines. The viruses at these loci are shown to be biologically distinguishable. The first, described previously, codes for activation of a virus that grows preferentially in NIH Swiss embryo cells. The newly detected locus codes for activation of a virus that grows poorly, if at all, in NIH Swiss or BALB/c cells, but replicates well in a rat cell line. Its serologic properties are different from those of viruses of the two major serologic subgroups of murine leukemia virus. The present findings provide support for the hypothesis that the loci for virus induction in BALB/c cells represent genetic information for C-type viruses and that the endogenous viruses are subject to different cellular genetic controls.