Binding properties of human immunodeficiency virus type-2 (HIV-2) RNA corresponding to the packaging signal to its nucleocapsid protein.

The nucleocapsid (NC) protein of human immunodeficiency virus type-1 (HIV-1) contains two zinc finger motifs (ZFMs), and binds specifically to the packaging signal which is located in the 5' leader sequence of the viral genomic RNA between the first splice donor and the gag initiator codon (AUG). In this study, we analyzed the specificity of the binding of the corresponding region of HIV-2 (Region 3) to its NC protein (NCp8), by performing a competitive ultraviolet (UV) cross-linking assay using in vitro-synthesized 32P-labeled and unlabeled RNAs corresponding to a sequence between the primer binding site and the gag AUG (Region 1). Binding of 32P-labeled Region 1 RNA to NCp8 was inhibited specifically by adding unlabeled Region 1 and 3 RNAs and no specific binding was detected using deletion mutant peptides of NCp8. These findings suggest that the region(s) which bind(s) specifically to HIV-2 NCp8 lie(s) between the first splice donor and the gag AUG in the 5' leader sequence and that NCp8 is the minimum binding region responsible for the specific binding of the region downstream of the first splice donor site of HIV-2 RNA.