| The defining feature of all retroviruses is the ability to replicate by reverse-transcribing viral RNA into double-stranded DNA for integration into the host genome. Reverse transcription initiation requires a host tRNA primer that is complementary to and binds the primer binding site (PBS) in the viral U5. HIV-1 has evolved to exclusively use tRNALys,3. How and why HIV-1 preferentially selects this primer for replication is the focus of this study.; Previous studies in continuous T cell lines have shown that changing the PBS to be complimentary to the 3' end of an alternate tRNA can force the temporary use of this primer. However, the virus quickly reverts to use tRNA Lys,3. The U5 A - loop, upstream of the PBS, forms a stem-loop structure that interacts with the anticodon of the tRNA primer. Viruses with both U5 and PBS mutations are more stable for use of an alternate primer.; This study investigates tRNA selection in primary T cells, which more closely resemble the natural target of HIV-1. Peripheral blood mononuclear cells (PBMC) were infected with HIV containing U5 and PBS sequences complementary to the 3' end and anticodon loop of tRNAHis, tRNA Lys1,2, tRNAPro, tRNAMet, or tRNA Ile, respectively. Viruses with PBS mutations alone reverted to use tRNALys,3, while viruses with additional U5 mutations remained stable. Interestingly, virus with PBS changes made to be complementary to tRNAMet maintained use of this primer with or without additional U5 changes. Conversely, virus with a PBS made to be complementary to tRNA Ile rapidly reverted to tRNALys,3, regardless of the US sequence.; These studies have revealed a preference by HIV-1 for selection of certain tRNA primers and that this selection is influenced by the availability of tRNAs in different cell types. Recent studies have shown that HIV-1 only selects tRNA primers that have been exported from the nucleus and have been incorporated in the protein synthesis pathway. A possible explanation for these observations is that tRNA selection intersects with viral protein synthesis in the cell. Further understanding of this process may reveal new drug therapy targets. |
