title: PreQ1-II riboswitch
text: # PreQ1-II riboswitch
  
  PreQ1-II riboswitches form a class of riboswitches that specifically bind $pre-queuosine_1$ $(PreQ_1),$ a precursor of the modified nucleoside queuosine. They are found in certain species of Streptococcus and Lactococcus, and were originally identified as a conserved RNA secondary structure called the "COG4708 motif". All known members of this riboswitch class appear to control members of COG4708 genes. These genes are predicted to encode membrane-bound proteins and have been proposed to be a transporter of $preQ_1,$ or a related metabolite, based on their association with $preQ_1-binding$ riboswitches. PreQ1-II riboswitches have no apparent similarities in sequence or structure to preQ1-I riboswitches, a previously discovered class of $preQ_1-binding$ riboswitches. $PreQ_1$ thus joins S-adenosylmethionine as the second metabolite to be found that is the ligand of more than one riboswitch class.
  
  