Cellular control of murine type C virus

Murine leukemia virus (MuLV) strains can be divided into three broad classes: ecotropic strains replicate preferentially in homologous cells; xenotropic strains preferentially replicate in heterologous cells, and amphotropic strains, isolated from feral mice, replicate efficiently in both heterologous and homologous cells. Hamster cells are nonpermissive for the replication of all three classes. The authors have investigated the cellular mechanisms restricting the replication of these three classes. Much of this work has involved the use of hybrid cells formed by the fusion of permissive cells of one species with nonpermissive cells of another species. The use of such hybrid cells offers many other advantages in studying the biology of RNA tumor viruses. They can be used to classify viruses, to identify the chromosomal location of genes coding for virus structure, surface receptors, and other functions essential for virus replication. They also help identify and localize the site of action of intracellular repressor substances. Some of these uses are illustrated in these studies.