Artificial induction of the UPR by Tet-off system-dependent expression of Hac1 and its application in Saccharomyces...

In response to endoplasmic reticulum (ER) stress, yeast Saccharomyces cerevisiae cells produce Hac1, which is a transcription factor responsible for the unfolded protein response (UPR). When Hac1 is unregulatedly expressed from a constitutive promoter, the ER is artificially enforced and enlarged, even without ER stress stimuli. However, such cells are unsuitable for applicative bioproduction because they grow quite slowly and quickly lose their high-UPR phenotype upon their long-term storage. To avoid this problem, we constructed S. cerevisiae plasmids for Hac1 expression under the control of the inducible Tet-off promoter. Yeast cells carrying these plasmids did not exhibit a considerable UPR and grew rapidly when the Tet-off promoter was repressed by doxycycline. In contrast, under the Tet-off inducing condition, these plasmids caused UPR induction, growth retardation, and ER expansion, depending on the copy number of the plasmid. Moreover, as expected, lipidic molecule production was increased under these conditions.