SEQUENCES IN THE REV-RESPONSIVE ELEMENT RESPONSIBLE FOR PREMATURE TRANSLATIONAL ARREST IN THE HUMAN-IMMUNODEFICIENCY-VIRUS-TYPE-1 ENVELOPE

Cell-free translation in the presence of pancreatic microsomal membran es of the full-length envelope transcript of the human immunodeficienc y virus type 1 (HIV-1) yielded the expected extensively glycosylated a nd immunologically reactive gp160 envelope-protein precursor. In addit ion to this gp160, a shorter glycoprotein, which we designated gp120, was produced due to a premature translation arrest. Utilizing kinetic experiments, pulse-chase analyses and various gp160 envelope RNA muta nts, we demonstrated that the in-vitro-produced gp120 was not formed by cleavage of the gp160 precursor or by internal initiation of transl ation. A gp120 produced before gp160 synthesis was completed, and, ind ependent of the gp160 proteolytic processing, has been shown to be pro duced and sequestered in the endoplasmic reticulum of HIV-1-infected c ells [Willey, R. L., Klimkait, T., Frucht, D. M., Bonifacino, J. S. & Martin, M. A. (1991) Virology 184, 319-329]. The specific translationa l 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 t wo contiguous putative stem loops of the Rev-responsive element, locat ed 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 respon sible for the production of alternative products by premature translat ional arrest in higher eukaryotes.