Identification and distinct regulation of three di/tripeptide transporters in Aspergillus oryzae.

The uptake of di/tripeptides is mediated by the proton-dependent oligopeptide transporter (POT) family. In this study, 3 POT family transporters, designated PotA, PotB, and PotC were identified in Aspergillus oryzae. Growth comparison of deletion mutants of these transporter genes suggested that PotB and PotC are responsible for di/tripeptide uptake. PotA, which had the highest sequence similarity to yeast POT (Ptr2), contributed little to the uptake. Nitrogen starvation induced potB and potC expression, but not potA expression. When 3 dipeptides were provided as nitrogen sources, the expression profiles of these genes were different. PrtR, a transcription factor that regulates proteolytic genes, was involved in regulation of potA and potB but not in potC expression. Only potC expression levels were dramatically reduced by disruption of ubrA, an orthologue of yeast ubiquitin ligase UBR1 responsible for PTR2 expression. Expression of individual POT genes is apparently controlled by different regulatory mechanisms.