Relationship of infectious murine leukemia virus and virus-related antigens in genetic crosses between AKR and the Fv-1 compatible strain C57L.

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Abstract
In a further genetic study of murine leukemia virus (MuLV) and its components the backcross C57L .times. (C57L .times. AKR) was studied. This population was selected because strains AKR and C57L are Fv-1n, and the restriction which the Fv-1b allele imposes on the output of virus was obviated. The segregants were scored for 3 characters: infectious Gross-AKR-type MuLV (V) in the tail, group-specific antigen indicative of p30 internal viral protein in spleen and GIX antigen, now thought to be indicative of gp69/71 viral envelope glycoprotein, on thymocytes. The AKR mouse has 2 unlinked chromosomal genes, Akv-1 and Akv-2, each of which can independently give rise to the life-long high output of MuLV that is characteristic of AKR mice. Of the 8 phenotypes that could possibly be derived from segregation of the 3 pairs of independent alternative traits, 7 were observed, but on progeny testing only 3 reflected stably heritable genotypes. These were V+p30+GIX+ and V-p30-GIX- (the parental types) and V-p30+GIX+. A 3rd, newly identified AKR gene, designated Akup, segregating independently of Akv-1 and Akv-2, also determines expression of p30 and GIX but in this case independently of XC-detectable MuLV. The 4 remaining observed phenotypes, which did not breed true on progeny testing, involved antigen-negative parents yielding antigen-positive progeny. These discrepancies probably represented suppression of the phenotype by a maternal resistance factor.