PreQ1-III riboswitch

Consensus secondary structure of PreQ₁-III riboswitches, based on earlier data than a previously published depiction.^[1] The structural significance of the pairing interaction labeled "pseudoknot or alternate stem" is currently unknown. The P1 stem is unusually rich in A and U nucleotides, but is supported by experimental data.

PreQ1-III riboswitches are a class of riboswitches that bind pre-queuosine₁ (PreQ₁), a precursor to the modified nucleoside queuosine.^[1] PreQ₁-III riboswitches are the third class of riboswitches to be discovered that sense this ligand, and are structurally distinct from preQ₁-I and preQ₁-II riboswitches. Most sequenced examples of preQ₁-III riboswitches are obtained from uncultivated metagenome samples, but the few examples in cultivated organisms are present in strains that are known to or suspected to be Faecalibacterium prausnitzii, a species of Gram-positive Clostridia. Known examples of preQ₁-III riboswitches are found upstream of queT genes, which are expected to encode transporters of a queuosine derivative. The other two known classes of preQ₁ riboswitches are also commonly found upstream of queT genes.

The atomic-resolution structure of a preQ1-III riboswitch has been solved by X-ray crystallography.^[2]

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