Selective optimization of the Rev-binding element of HIV-1

RNA molecules that can bind to the Rev protein of HIV-1 have been isolated from random sequence nucleic acid pools based on a minimal Rev-binding element (RBE) found within the Rev Responsive Element (RRE). While the selected sequences are related to the wild-type element, they also contain substitutions that allow them to bind Rev up to 10-fold better in vitro. A hypothesized homopurine pairing at G48:G71 is generally replaced by A48:A71; the occasional selection of C48:A71 suggests that R71 may be in a syn conformation. These data support the structural model for the RBE originally proposed by Bartel ef a/. (1). Additional interactions with the Rev protein are promoted by the sequence CUC... UYGAG, found in one class of high-affinity aptamers, but absent from the wild-type element. Within each class of aptamers different residues and substructures covary with one another to generate optimal Rev-binding surfaces. The interdependencies of different nucleotide substitutions suggest structural models for both the wild-type RBE and the selected high-affinity aptamers