Structure of a class II preQ 1 riboswitch reveals ligand recognition by a new fold

PreQ 1 , a metabolic precursor of the modified tRNA nucleotide queuosine, regulates expression of queuosine biosynthetic genes via two distinct classes of preQ 1 riboswitch. Biochemical studies and the first X-ray crystal structure of a class II preQ 1 riboswitch reveal how preQ 1 recognizes this RNA motif and how it may regulate translation of downstream genes.