Tetraloop

Tetraloops are a type of four-base hairpin loop motifs in RNA secondary structure that cap many double helices. There are many variants of the tetraloop, the published ones include ANYA, CUYG, GNRA, UMAC and UNCG.

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. Tetraloops with the sequence UMAC have essentially the same backbone fold as the GNRA tetraloop, but may be less likely to form tetraloop-receptor interactions. They may therefore be a better choice for closing stems when designing artificial RNAs.