RNA structure: Tetraloops

Abstract

RNA hairpins are among the most common RNA secondary structural elements and are frequently capped by RNA tetraloops. RNA tetraloops are composed of characteristic four-loop nucleotides that form a compact and stable structure. While they can be formed by many different nucleotide sequences, UNCG (N？=？A, C, G, or U), GNRA (R？=？A or G), and CUUG tetraloops are found most often. Tetraloops usually help initiate RNA-folding processes and provide sites for tertiary contacts within or between RNAs and for protein binding, thereby facilitating the assembly of ribonucleoprotein particles. Tetraloop interactions can be either sequence- or structure-specific. Herein, we discuss the structures of RNA tetraloops and their interactions with other RNA structural motifs and with RNA-binding proteins.