TRANSLATIONAL FRAMESHIFTING AT THE GAG-POL JUNCTION OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 IS NOT INCREASED IN INFECTED T-LYMPHOID CELLS

A frameshift event is necessary for expression of the products of the pol gene in a number of retroviruses, including human immunodeficiency virus type 1 (HIV-1). The basic signals necessary for frameshifting c onsist of a shifty sequence in which the ribosome slips and a downstre am stimulatory structure which can be either a stem-loop or a pseudokn ot. In HIV-1, much attention has been paid to the frameshift site itse lf, and only recently has the role of the downstream structure been ex amined. Here we used a luciferase-based experimental system to analyze in vivo the cis and trans factors potentially involved in controlling frameshifting efficiency at the gag-pol junction of HIV-1. We demonst rated that high-level frameshifting is dependent on the presence of a palindromic region located downstream of the site where the frameshift event takes place. Frameshifting efficiencies were found to be identi cal in mouse fibroblasts and the natural host cells of the virus, i.e. , CD4(+) human lymphoid cells. Furthermore, no increase in frameshifti ng was observed upon virus infection. Previous observations have shown that viral infection leads to specific alteration of tRNAs involved i n translation of shifty sites (D. Hatfield, Y.-X. Feng, B.J. Lee, A. R ein, J.G. Levin, and S. Oroszlan, Virology 173:736-742, 1989). The res ults presented here strongly suggest that these modifications do not a ffect frameshifting efficiency.