ABSTRACT
An essential step in the replication of all retroviruses is the capture of a cellular tRNA that is used as the primer for reverse transcription. The 3′-terminal 18 nucleotides of the tRNA are complementary to the primer binding site (PBS). Moloney murine leukemia virus (MuLV) preferentially captures tRNAPro. To investigate the specificity of primer selection, the PBS of MuLV was altered to be complementary to different tRNAs. Analysis of the infectivity of the virus and stability of the PBS following in vitro replication revealed that MuLV prefers to select tRNAPro, tRNAGly, or tRNAArg. Previous studies from our laboratory have suggested that tRNA primer capture is coordinated with translation. Coincidentally, a cluster of proline, arginine, and glycine precedes the Gag-Pol junction of MuLV. Human immunodeficiency virus type 1 (HIV-1), which prefers
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as the primer, can be forced to utilize tRNAMet,
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, tRNAHis, or tRNAGlu, although these viruses replicate poorly. Codons for methionine, lysine, histidine, or glutamic acid are found prior to the Gag-Pol frameshift site. HIV-1 was mutated so that the 5 lysine codons prior to the Gag-Pol frameshift region were specific for
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. HIV-1 forced to use
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as the primer, with the mutation of codons specific for
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prior to the Gag-Pol junction, had enhanced infectivity and replicated similarly to the wild-type virus. The results demonstrate that codon preference prior to the Gag-Pol junction influences primer selection and suggest a coordination of Gag-Pol synthesis and acquisition of the tRNA primer required for retrovirus replication.
Identification and Characterization of an Exogenous Retrovirus from Atlantic Salmon Swim Bladder Sarcomas
