Translation elongation factor 1-alpha interacts specifically with the human immunodeficiency virus type 1 Gag polyprotein

Human immunodeficiency virus type 1 (HIV-1) gag-encoded proteins play key f unctions at almost all stages of the viral life cycle. Since these function s may require association with cellular factors, the HIV-1 matrix protein ( MA) was used as bait in a yeast two-hybrid screen to identify MA-interactin g proteins. MA was found to interact with elongation factor 1-alpha (EF1 al pha), an essential component of the translation machinery that delivers ami noacyl-tRNA to ribosomes. EF1 alpha was then shown to bind the entire HIV-1 Gag polyprotein. This interaction is mediated not only by Mk, but also by the nucleocapsid domain, which provides a second, independent EF1 alpha-bin ding site on the Gag polyprotein. EF1 alpha is incorporated within HIV-1 vi rion membranes, where it is cleaved by the viral protease and protected fro m digestion by exogenously added subtilisin. The specificity of the interac tion is demonstrated by the fact that EF1 alpha does not bind to nonlentivi ral MAs and does not associate with Moloney murine leukemia virus virions. The Gag-EF1 alpha interaction appears to be mediated by RNA, in that basic residues in MA and NC are required for binding to EF1 alpha, RNase disrupts the interaction, and a Gag mutant with undetectable EF1 alpha-binding acti vity is impaired in its ability to associate with tRNA in cells. Finally, t he interaction between MA and EF1 alpha impairs translation in vitro, a res ult consistent with a previously proposed model in which inhibition of tran slation by the accumulation of Gag serves to release viral RNA from polysom es, permitting the RNA to be packaged into nascent virions.