Research Projects

Pichia pastoris, a methylotrophic and respiratory yeast, has been used for the commercial production of recombinant proteins. The PI has been investigating the regulation of carbon metabolism in P. pastoris, characterized several transcription factors, and identified a novel, glutamate-inducible, post-transcriptional regulatory circuit. Rtg1p, a basic helix-loop-helix (bHLH-Zip) protein, plays a key role in this regulation. In S. cerevisiae, Rtg1p heterodimerizes with another bHLH-Zip protein, Rtg3p, which regulates the expression of genes of the retrograde response pathway. The previous SERB project demonstrated that Rtg3p is absent in P. pastoris and acts as a cytosolic, post-transcriptional regulator of glutamate dehydrogenase (GDH2) and phosphoenolpyruvate carboxykinase (PEPCK) in cells cultured in media containing glutamate as the sole source of carbon and nitrogen. The 5' UTR of GDH2 mRNA has a key role to investigate in detail. The researchers also wish to characterize two other P. pastoris Rtg proteins, Rtg2p and RtgXp. Rtg2p, a bHLH protein lacking a leucine zipper, is renamed RtgXp and localizes to the nucleus in cells cultured in ethanol and methanol but cytosolic in cells metabolizing glutamate. The study aims to understand the nuclear and cytosolic functions of RtgXp and use the GDH2 and PEPCK promoters for glutamate-inducible synthesis of recombinant proteins in P. pastoris.