Thymotropic envelope gene recombinants of Moloney leukemia virus have highly conserved envelope structures

Envelope gp70s were isolated from the thymotropic recombinant viruses related to Moloney murine leukemia virus (RM-M-MuLVs) which were generated by the inoculation of two strains of ecotropic M-MuLV (strain 1869 and temperature-sensitive mutant-1) into BALB/c or CFW/D mice. Chymotrypsin oligopeptide maps of parental ecotropic MuLV, RM-M-MuLV, and inducible xenotropic MuLV showed each of the above virus types had a distinctly characteristic peptide map. The majority of RM-M-MuLV gp70 molecules examined showed a high degree of peptide homology. Data from restriction endonuclease mapping demonstrated that the newly acquired sequences in each of the RM-M-MuLVs were very related and encompassed both the polymerase and the envelope genes. The source of the sequences acquired by the RM-M-MuLV was from endogenous nonecotropic and nonxenotropic proviruses. This suggested that the family of endogenous proviruses which combined with the parental ecotropic virus was either specifically selected or was much more available than other endogenous proviruses. Although slight variations of envelope-specific sequences and peptides existed among various RM-M-MuLV isolates; within a single thymoma, individual clones of tumor cells yielded RM-M-MuLV gp70s which were identical to each other. These findings are discussed within the context of the leukemogenic potential of RM-MuLVs.