IDENTIFICATION OF A BINDING-SITE FOR THE HUMAN-IMMUNODEFICIENCY-VIRUSTYPE-1 NUCLEOCAPSID PROTEIN

The nucleocapsid (NC) protein NCp7 of human immunodeficiency virus typ e 1 (HIV-1) is important for encapsidation of the virus genome, RNA di merization, and primer tRNA annealing in vitro. Here we present eviden ce from gel mobility-shift experiments indicating that NCp7 binds spec ifically to an RNA sequence. Two complexes were identified in native g els. The more slowly migrating complex contained two RNA molecules and one peptide, while the more rapidly migrating one is composed of one RNA and one peptide. Further, mutational analysis of the RNA shows tha t the predicted stem and loop structure of stem-loop 1 plays a critica l role. Our results show that NCp7 binds to a unique RNA structure wit hin the psi region; in addition, this structure is necessary for RNA d imerization. We propose that NCp7 binds to the RNA via a direct intera ction of one zinc-binding motif to stem-loop 1 followed by binding of the other zinc-binding motif to stem-loop 1, stem-loop 2, or the linke r region of the second RNA molecule, forming a bridge between the two RNAs.