Members of this protein family have been assigned as thiamine transporters by a phylogenetic analysis of families of genes regulated by the THI element, a broadly conserved RNA secondary structure element through which thiamine pyrophosphate (TPP) levels can regulate transcription of many genes related to thiamine transport, salvage, and de novo biosynthesis. Species with this protein always lack the ThiBPQ ABC transporter. In some species (e.g. Streptococcus mutans and Streptococcus pyogenes), yuaJ is the only THI-regulated gene. Evidence from Bacillus cereus indicates thiamine uptake is coupled to proton translocation.