Isolation of a recombinant murine leukemia virus utilizing a new primer tRNA.

We have previously described the construction of a mutant of Moloney murine leukemia virus bearing a deletion at the normal site of integration of the viral DNA. We have now recovered a revertant of the virus after abortive infection of mouse cells and have determined the structure of the new virus. The revertant is a recombinant virus containing a 500-base-pair patch of new sequences derived from the mouse genome. The integration site was perfectly restored to the wild-type sequence, although the patch of DNA was overall only 80% homologous to Moloney murine leukemia virus. Surprisingly, the tRNA primer binding site was no longer homologous to the usual proline tRNAs, but was a perfect match for glutamine tRNA. This result suggests that the Moloney murine leukemia virus reverse transcriptase is not specific to one tRNA, but can utilize different tRNAs to prime the synthesis of viral DNA. Comparisons with published reports allowed the identification of sequences that are 94% homologous to the patch sequence, present in one of the endogenous retroviral sequences of the mouse. No replication-competent members of this family, utilizing the glutamine tRNA primer, have been previously isolated.