TPP riboswitch (THI element)

In molecular biology, the THI element is a highly conserved RNA secondary structure. It serves as a riboswitch that binds directly to thiamine pyrophosphate (TPP) to regulate gene expression through a variety of mechanisms in archaea, bacteria and eukaryotes. TPP is the active form of thiamine (vitamin B1), an essential coenzyme synthesised by coupling of pyrimidine and thiazole moieties in bacteria. The THI element is an extension of a previously detected thiamin-regulatory element, thi box. Analysis of operon structures has identified a large number of new candidate thiamin-regulated genes, mostly transporters, in various prokaryotic organisms.