Riboswitch sequences (in the mRNA leader transcript) bind molecules such as amino acids, nucleotides, sugars, vitamins, metal ions and other small ligands which cause a conformational change in the mRNA. Most of these attenuators are inhibitory and are employed by genes for biosynthetic enzymes or transporters whose expression is inversely related to the concentration of their corresponding metabolites.
Example- Cobalamine biosynthesis, Cyclic AMP-GMP switch, lysin biosynthesis, glycine biosynthesis, fluroide switch etc.