Stem-loop

Stem-loops are nucleic acid secondary structural elements which form via intramolecular base pairing in single-stranded DNA or RNA.

The first prerequisite is the presence of a sequence that can fold back on itself to form a paired double helix.

One common loop with the sequence UUCG is known as the "tetraloop," and is particularly stable due to the base-stacking interactions of its component nucleotides.

The self-cleaving hammerhead ribozyme contains three stem-loops that meet in a central unpaired region where the cleavage site lies.

[3] The mRNA stem-loop structure forming at the ribosome binding site may control an initiation of translation.