In a chain-like biological molecule, such as a protein or nucleic acid, a structural motif is a common three-dimensional structure that appears in a variety of different, evolutionarily unrelated molecules.
[1] A structural motif does not have to be associated with a sequence motif; it can be represented by different and completely unrelated sequences in different proteins or RNA.
Depending upon the sequence and other conditions, nucleic acids can form a variety of structural motifs which is thought to have biological significance.
Note that, while the spatial sequence of elements may be identical in all instances of a motif, they may be encoded in any order within the underlying gene.
Structural motifs may also appear as tandem repeats.