A central question in HIV infection is how viral RNA is specifically recognized and packaged into virions. Encapsidation of HIV-1 is a multistep process which involves recognition, selection, dimerization and packaging. Recent studies have clearly demonstrated that this process is governed by specific interactions between the nucleocapsid domain (NCp7) of gag and the encapsidation-dimerization linker sequence (E-DLS). We have shown by extensive computer analysis and RNase mapping that the retroviral E-DLS can be folded into stem and loop structures; disruption of part or all of these RNA structures can impair packaging. The NC proteins of HIV-1 contain two copies of a Cys-X2-Cys-X4-His-X4-Cys sequence referred to as """"""""CCHC"""""""" Zinc-finger motif. The three dimensional structure of the two zinc finger motifs of NCp7 from HIV-1 shows that each finger folds independently when in coordination with Zn 2+. The binding site on HIV-1 viral RNA recognized by NCp7 is called the packaging site, Psi. The Psi site is located upstream of the gag translation initiation codon and includes the splice donor site and a highly conserved purine rich region. A chemical interference analysis mapped the nucleotides critical for NCp7 binding to a region of 4 nucleotides located within a single stem-loop structure. Elucidation of the molecular details required for HIV-1 encapsidation has given impetus to new approaches for the design of anti-viral agents. Several disulfide benzamides have been shown to eject HIV-1 NCp7 zinc from purified virions and to possess anti-retroviral activity in cell cultures at low micromolar concentrations (Rice et al. Nature 361: 473, 1993; Rice et al. Science 270: 1194, 1995). New congeners of the disulfide benzamide series are under intense investigation in our laboratory and should provide new compounds with potential therapeutic value and should function to block HIV-1 encapsidation and efficient assembly of infectious virions. These drugs directed at highly conserved targets should be effective against all serotypes and mutants of HIV-1 and should not be susceptible to drug resistance.
