Members of this family are found in all the three major phyla of life: archaebacteria, eubacteria, and eukaryotes. In Bacillus subtilis, TENA is one of a number of proteins that enhance the expression of extracellular enzymes, such as alkaline protease, neutral protease and levansucrase. The THI-4 protein, which is involved in thiamine biosynthesis, is also a member of this family. The C-terminal part of these proteins consistently show significant sequence similarity to TENA proteins. This similarity was first noted with the Neurospora crassa THI-4. This family includes bacterial coenzyme PQQ synthesis protein C or PQQC proteins. Pyrroloquinoline quinone (PQQ) is the prosthetic group of several bacterial enzymes,including methanol dehydrogenase of methylotrophs and the glucose dehydrogenase of a number of bacteria. PQQC has been found to be required in the synthesis of PQQ but its function is unclear. The exact molecular function of members of this family is uncertain.