Regulation of Pichia pastoris promoters and its consequences for protein production

The methylotrophic yeast Pichia pastoris is a widely used host for heterologous protein production. Along with favorable properties such as growth to high cell density and high capacities for protein secretion, P. pastoris provides a strong, methanol inducible promoter of the alcohol oxidase 1 (AOX1) gene. The regulation of this promoter has been extensively studied in recent years by characterizing cis-acting sequence elements and trans-acting factors, revealing insights into underlying molecular mechanisms. However, new alternative promoters have also been identified and characterized by means of their transcriptional regulation and feasibility for protein production using P. pastoris. Besides the often applied GAP promoter, these include a variety of constitutive promoters from housekeeping genes (e.g. TEF1, PGK1, TPI1) and inducible promoters from particular biochemical pathways (e.g. PHO89, THI11, AOD). In addition to these promoter sequence/function based studies, transcriptional regulation has also been investigated by characterizing transcription factors (TFs) and their modes of controlling bioprocess relevant traits. TFs involved in such diverse cellular processes such as the unfolded protein response (UPR) (Hac1p), iron uptake (Fep1p) and oxidative stress response (Yap1p) have been studied. Understanding of these natural transcriptional regulatory networks is a helpful basis for synthetic biology and metabolic engineering approaches that enable the design of tailor-made production strains.