are a type of four-base hairpin loop
motifs in RNA
secondary structure that cap many double helices. Three types of tetraloops are common in ribosomal RNA: GNRA, UNCG and CUUG. The GNRA tetraloop has a guanine-adenine base-pair where the guanine is 5' to the helix and the adenine is 3' to the helix.
- Woese CR, Winkers S, Gutell RR (1990). "Architecture of ribosomal RNA: Constraints on the sequence of "tetra-loops"". Proc. Nati. Acad. Sci. USA 87 8467–71.