Genetic evidence for a product of the Fv-1 locus that transfers resistance to mouse leukemia viruses

Abstract

Extracts of mouse cells have been shown to transfer resistance to Nor Btropic host range types of mouse leukemia viruses. The genetic specificity of the inhibition was tested in two ways: (i) by correlating the Fv-1 genotype of a number of mouse strains with the restriction-transferring activity of extracts of the respective embryo cell cultures, and (ii) by correlating the Fv-1 genotype of B6C3F2 (C57BL/6 Y [Fv-lbb] by C3H d [Fv-101] parental strains) mouse embryos, which segregate the Fv-1 alleles in a 1:2:1 ratio, with the inhibitor activity of extracts of the cells from each embryo. Five independent matings, totaling 45 individual embryos, were tested. Each embryo was cultured, and the Fv-1 genotype was determined independently by titration of N-and' B-tropic viruses; the extracts of replicate secondary cultures were tested for their effect on infection of permissive cells by N-and B-tropic viruses. The specific-restrictiontransferring activity of the embryos was found to segregate with the appropriate Fv-1 genotype. These results confirm the suggestion that the inhibitor of the leukemia virus host range types in the cellular extracts is a product of the Fv-1 locus.

Transfer of Fv-1 locus-specific resistance to murine N-tropic and B-tropic retroviruses by cytoplasmic RNA

“…missive mouse cells with cell-free extracts (44). Genetic analysis demonstrated that the resistance transfer activity of the cell extracts segregated specifically with the corresponding Fv-1 allele of mouse embryo cells (43). The present investigation demonstrates that RNA is the active component responsible for this transfer of Fv-1 gene-specific resistance.…”

“…Subeellular localization. We previously reported the transfer of Fv-1 gene resistance properties using cell-free extracts prepared by mild sonic disruption of cultured embryo cells (43,44). In our experience, inhibition of 20% or less may represent nonspecific activity, and only those fractions demonstrating greater inhibition were considered active; they were considered specific only if the inhibitory activity was directed against the appropriate virus.…”

“…Previous studies demonstrated that specific resistance could be transferred to pernissive cells by use of cell-free extracts (44). Genetic analysis of the resistance transfer has provided evidence that the effect is specific for the appropriate host-range type of virus and the Fv-1 genotype of cells used for preparation of the extracts (43). These results suggest that resistant cells constitutively synthesize a product which restricts competent proviral DNA formation.…”

“…Bioassay of Fv-1-specific gene products. Cell-free extracts and RNA were tested for their ability to transfer specific Fv-1 locus resistance properties into susceptible cells, essentially as previously described (43,44). Because of the complexity of the system for assaying the Fv-1-specific RNA, and also to obtain a high degree of reproducibility, stringent control was maintained over the many variables of the assay.…”

“…Preparation and fractionation of cell homogenate. Crude cell extracts of secondary mouse embryo cell cultures were prepared by sonic disruption as previously described (43,44). However, for the purpose of subcellular localization of Fv-I-specific activity, cell homogenates were made under aseptic conditions by the following procedure.…”