The proline-dependent transcription factor Put3 regulates the expression of the riboflavin transporter MCH5 in Saccharomyces cerevisiae.

Like most microorganisms, the yeast Saccharomyces cerevisiae is prototrophic for riboflavin (vitamin B2). Riboflavin auxotrophic mutants with deletions in any of the RIB genes frequently segregate colonies with improved growth. We demonstrate by reporter assays and Western blots that these suppressor mutants overexpress the plasma-membrane riboflavin transporter MCH5.

The monocarboxylate transporter homolog Mch5p catalyzes riboflavin (vitamin B2) uptake in Saccharomyces cerevisiae.

Riboflavin is a water-soluble vitamin (vitamin B2) required for the production of the flavin cofactors FMN and FAD. Mammals are unable to synthesize riboflavin and need a dietary supply of the vitamin. Riboflavin transport proteins operating in the plasma membrane thus have an important role in the absorption of the vitamin.