PreQ1-III riboswitches are a class of

riboswitch In molecular biology, a riboswitch is a regulatory segment of a messenger RNA molecule that binds a small molecule, resulting in a change in production of the proteins encoded by the mRNA. Thus, an mRNA that contains a riboswitch is directly invo ...

es that bind pre-queuosine₁ (PreQ₁), a precursor to the modified nucleoside

queuosine Queuosine is a modified nucleoside that is present in certain tRNAs in bacteria and eukaryotes. It contains the nucleobase queuine. Originally identified in ''Escherichia coli, E. coli'', queuosine was found to occupy the first anticodon position ...

. 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 Metagenomics is the study of genetic material recovered directly from environmental or clinical samples by a method called sequencing. The broad field may also be referred to as environmental genomics, ecogenomics, community genomics or microb ...

samples, but the few examples in cultivated organisms are present in strains that are known to or suspected to be ''

Faecalibacterium prausnitzii ''Faecalibacterium'' is a genus of bacteria. Its sole known species, ''Faecalibacterium prausnitzii'' is gram-positive, mesophilic, rod-shaped, anaerobic and is one of the most abundant and important commensal bacteria of the human gut microbiota ...

'', a species of

Gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacte ...

Clostridia The Clostridia are a highly polyphyletic class of Bacillota, including '' Clostridium'' and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them. Sp ...

. 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.

References

Cis-regulatory RNA elements Riboswitch {{molecular-cell-biology-stub