Genetics of xenotropic virus expression in mice. I. Evidence for a single locus regulating spontaneous production of infectious virus in crosses involving NZB/B1NJ and 129/J strains of mice.

The extent of infectious xenotropic virus expression in homogenized splenic tissues from the high-virus-expressing NZB/BINJ mice and the non-virus-expressing 129/J mice and their crosses has been examined. The data suggest that a single autosomal "dominant-like" gene controls the spontaneous production and release of infectious xenotropic virus in NZB mice. Analysis of infectious virus production in second-backcross families [(F1 X 129) X 129] confirmed this conclusion. Variations in the amount of X-tropic virus released were evident in all genetic crosses. Virus titers (expressed as focus-forming units per milliliter) of supernatant fluid ranged from high levels in the NZB mice to somewhat lower levels in crosses involving the 129 mice. In the absence of a definite pattern in the titers observed in the genetic crosses studied, the term dominant-like is proposed for the single gene regulating the expression of X-tropic virus in NZB mice.