Sequences in the rev‐responsive element responible for premature translational arrest in the human‐immunodeficiency‐virus‐type‐1 envelope

Cell‐free translation in the presence of pancreatic microsomal membranes of the full‐lenght envelope transcript of the human immunodeficiency virus type 1 (HIV‐1) yielded the expected extensively glycosylated and immunologically reactive gp 160 envelope‐protein precursor. In addition to this gp160, a shorter glycoprotein, which we designated gp120*, was produced due to a premature translation arrest. Utilizing kinetic experiments, pulse‐chase and analyses and various gp160 envelope RNA mutants, we demonstrated that the in‐vitro ‐produced gp120* was not formed by cleavage of the gp160 precursor or by internal initiation of translation. A gp120 produced before gp160 synthesis was completed, and, independent of the gp160 proteolytic processing, has been shown to be produced and sequestered in the endoplasmic reticulum of HIV‐1‐infected cells [Willey, R. L., Klimkait, T., Frucht, D. M., Bonifacino, J. S. & Martin, M. A. (1991) Virology 184 , 319–329]. The specific translational arrest shown to occur in vitro was found to be dependent on the Rev‐responsive element, since deletion of this highly structured sequence abolished the production of gp120*. We found that the combination of two contiguous putative stem loops of the Rev‐responsive element, located at nucleotides 7494–7522 and 7525–7550 of the HIV‐1 Rev‐responsive‐element sequence, was responsible for the production of this truncated protein. To our knowledge, these stem‐loop structures, distinct from that known to bind the Rev protein, represent the first example responsible for the production of alternative products by premature translational arrest in higher eukarytes.