The PreQ1-I riboswitch is a cis-acting element identified in bacteria which regulates expression of genes involved in biosynthesis of the nucleoside queuosine (Q) from GTP.

PreQ1-III riboswitch has an atypically organized pseudoknot that does not appear to incorporate its downstream expression platform at its ribosome binding site (RBS).

[9] The first reported preQ1 riboswitch was located in the leader of the Bacillus subtilis ykvJKLM (queCDEF) operon which encodes four genes necessary for queuosine production.

[8] In this organism, PreQ1 binding to the riboswitch aptamer is thought to induce premature transcription termination within the leader to down-regulate expression of these genes.

[12] The preQ1 ligand is buried in the pseudoknot core and stabilized through intercalation between helical stacks and hydrogen bond interaction with heteroatoms.

[11] In presence of preQ1, the 3’ end of the adenine rich tail domain pairs with the center of P1 hairpin loop to form an H-type pseudoknot.

[13] Translation of protein in prokaryotes is initiated by binding of 30S ribosomal subunit to the Shine-Dalgarno (SD) sequence in mRNA.

[11] The translational riboswitch from bacteria Thermoanaerobacter tengcongensis (Tte) is observed to be transiently closed (pre-docked) in absence of preQ1, whereas in presence of preQ1 a fully docked state is adopted.