Cloning and characterization of hlF2, a human homologue of bacterial translation initiation factor 2, and its interaction with HIV-1 matrix

The cDNA for a human homologue (hIF2) of bacterial (bIF2) and yeast (yIF2) translation initiation factor two (IF2) has been identified during a screen for proteins which interact with HIV-1 matrix. The hIF2 cDNA encodes a 122 0-amino-acid protein with a predicted relative molecular mass of 139 kDa, t hough endogeneous hIF2 migrates anomalously on SDS/PAGE at 180 kDa. hIF2 ha s an extended N-terminus compared with its homologues, although its central GTP-binding domain and C-terminus are highly conserved, with 58% sequence identity with yIF2. We have confirmed that hIF2 is required for general tra nslation in human cells by generation of a point mutation in the P-loop of the GTP-binding domain. This mutant protein behaves in a transdominant mann er in transient transfections and leads to a significant decrease in the tr anslation of a reporter gene. hIF2 interacts directly with HIV-1 matrix and Gag in vitro, and the protein complex can be immunoprecipitated from human cells. This interaction appears to block hIF2 function, since purified mat rix protein inhibits translation in a reticulocyte lysate, hIF2 does not co rrespond to any of the previously characterized translation initiation fact ors identified in mammals, but its essential role in translation appears to have been conserved from bacteria to humans.