Structure and Function of the HTLV-1 pro-pol Frameshift Site

Human T‐cell leukemia virus type I (HTLV‐1) is a human retrovirus. Replication of retroviruses, such as HTLV, is dependent upon synthesis of viral structural and enzymatic proteins. Translation of HTLV's enzymatic proteins depends upon two ‐1 programmed ribosomal frameshifts. While ‐1 programmed ribosomal frameshifting and the slippery sequences of the HTLV‐1 gag‐pro and pro‐pol frameshift sites have been established, the frameshift efficiencies and the structures within these sites have not been determined. Each frameshift site includes a heptanucleotide slippery sequence followed by a downstream RNA structure. In HTLV‐1's pro‐pol frameshift site, a pseudoknot structure is predicted downstream of the UUUAAAC slippery sequence. We hypothesize that this pseudoknot structure contributes significantly to frameshift efficiency. To test this hypothesis, we designed three variant frameshift sites, each of which disrupts a helix important to the pseudoknot structure. We report the in vitro frameshift efficiencies for the wild‐type and three variant HTLV pro‐pol frameshift sites. These efficiencies were measured using an in vitro dual‐luciferase frameshift assay. Preliminary data suggest that the pseudoknot structure is important to frameshifting.