Interference grouping of murine leukemia viruses: A distinct receptor for the MCF-Recombinant viruses in mouse cells

Abstract

Fourteen different isolates of mink cell focus-inducing (MCF) murine leukemia viruses (MuLV) were characterized with respect to viral interference on NIH/3T3 cells. I assayed viral interference by measuring the reduction in focus formation by murine sarcoma virus pseudotypes on cells chronically infected with MuLV. Although the MCFs interfered with each other in all combinations tested, there was no significant cross-interference between MCF and ecotropic MuLVs. These results imply that MCFs and ecotropic MuLVs enter NIH/3T3 cells via different receptors. Using a recombinant constructed in vitro by C. Holland and N. Hopkins, I also found that the receptor specificity of MuLV is determined by sequences to the 5′ side of 7.7 kbp (measured from the 5' end of the provirus). The distinct receptor specificity of MCF9 suggests that they may be recombinants in which the nonecotropic parent is not xenotropic MuLV, as originally proposed, but rather endogenous env sequences which are not part of nondefective viral genomes. The MCF receptor specificity may be encoded directly by these sequences. I also suggest that interference may have a profound effect on the dynamics of viral replication in vivo.