It serves as a riboswitch[1][2] that binds thiamine pyrophosphate (TPP) directly and modulates gene expression through a variety of mechanisms in archaea, bacteria and eukaryotes.

[3][4][5] 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, the thi box, there is considerable variability in the predicted length and structures of the additional and facultative stem-loops represented in dark blue in the secondary structure diagram [6] Analysis of operon structures has identified a large number of new candidate thiamin-regulated genes, mostly transporters, in various prokaryotic organisms.

[7] The x-ray crystal structure of the TPP riboswitch aptamer has been solved.

[8] This molecular or cell biology article is a stub.