An Arg/Lys-rich core peptide mimics TRBP binding to the HIV-1 TAR RNA upper-stem/loop.

TRBP is a cellular protein that binds to the HIV-1 leader RNA, TAR. Circular dichroism experiments have shown that a 24 amino acid peptide (TR1), located within a dsRNA binding domain (dsRBD) of TRBP, binds TAR with a 3:1 stoichiometry, eliciting a conformational change involving base unstacking. The binding characteristics of synthetic structural variants of TAR indicate that guanine residues play a key role in the TR1-RNA interaction and that binding sites exist in the upper-stem/loop and lower stem region of TAR. Deletion analysis of TR1 has led to the identification of a 15 amino acid subpeptide (TR13) which is necessary and sufficient to bind to the high affinity upper-stem/loop binding site of TAR. Alanine scanning of TR13 has revealed that mutations in either Lys or Arg residues result in altered TAR-binding, and molecular modelling/docking experiments have shown that the two Arg residues of TR13 can interact with two appropriately spaced guanine residues in the upper-stem/loop of TAR. The TR13 lysine residues appear to be essential for maintaining structural integrity and the correct positioning of the Arg side-chains. We propose that TRBP binds TAR by means of a "2-G hook" motif and that the binding specificity of this particular member of the family of double-stranded RNA-binding proteins lies within the highly conserved dsRBD core motif. Finally, our results also suggest that TRBP may function in vivo by modifying the tertiary structure of TAR RNA. Copyright 1998 Academic Press.