Virological properties and nucleotide sequences of cas-E-type endogenous ecotropic murine leukemia viruses in south Asian wild mice, Mus musculus castaneus

Two types of endogenous ecotropic murine leukemia viruses (MuLVs), termed A KV- and Cas-E-type MuLVs, differ in nucleotide sequence and distribution in wild mouse subspecies. In contrast to AKV-type MuLV, Cas-E-type MuLV is no t carried by common laboratory mice. Wild mice of Mus musculus (M. m.) cast aneus carry multiple copies of Cas-E-type endogenous MuLV, including the Fv -4(r) gene that is a truncated form of integrated MuLV and functions as a h ost's resistance gene against ecotropic MuLV infection. Our genetic cross e xperiments showed that only the Fv-4(r) gene was associated with resistance to ecotropic F-MuLV infection. Because the spontaneous expression of infec tious virus was not detected in M. m. castaneus, we generated mice that did not carry the Fv-4(r) gene but did carry a single or a few endogenous MuLV loci. In mice not carrying the Fv-4(r) gene, infectious MuLVs were isolate d in association with three of six Cas-E-type endogenous MuLV loci. The iso lated viruses showed a weak syncytium-forming activity for XC cells, an int erfering property of ecotropic MuLV, and a slight antigenic variation. Two genomic DNAs containing endogenous Cas-E-type MuLV were cloned and partiall y sequenced. All of the Cas-E-type endogenous MuLVs were closely related, h ybrid-type viruses with an ecotropic env gene and a xenotropic long termina l repeat. Duplications and a deletion were found in a restricted region of the hypervariable proline-rich region of Env glycoprotein.