RNA recognition by an isolated α helix

A 17 amino acid peptide containing the arginine-rich region of the HIV Rev protein binds specifically to Rev response element (RRE) RNA. Even though it is highly charged, the peptide forms an α helix in solution, but only when its N- and C-termini are modified to provide favorable electrostatic interactions with the helix macrodipole. Binding affinity for IIB RNA (the primary binding site within the RRE) increases with α helix content, whereas nonspecific binding affinity is independent of helix content. Binding of mutant peptides demonstrates that one threonine, one asparagine, and four arginine side chains are important for sequence-specific recognition. Transactivation of the HIV LTR using Tat-Rev peptide hybrids and the RRE IIB site indicates that the peptide adopts an α-helical conformation in vivo. The results suggest that interactions with the RNA backbone may help to orient the α helix in the major groove of RNA.