Improvement of foreign protein production by constitutive UPR induction in Aspergillus niger var. awamori

A signalling pathway from ER to nucleus called the unfolded protein response (UPR) controls the expression of genes for several endoplasmic reticulum-resident (ER) chaperones and foldases. When the unfolded protein response pathway is active, a signal is transduced from the ER lumen to the transcription machinery in the nucleus. It has been shown that the yeast transcription factor mediating the UPR induction of the chaperone and foldase genes is Hac1p. The UPR-induced form of the A. niger var. awamori hacA cDNA was expressed in A. niger var. awamori strain producing Trametes versicolor laccase. For the overexpression of hacA, the induced form of the A. niger var.awamori hacA cDNA was first created by deleting the 20 bp intron and truncating the 5' flanking region by about 150 bp, which omitted the upstream open reading frame. The laccase activity measurements made from the supernatants show that all the transformants produce more laccase than the parental strain. The production levels of the transformants were in the fifth day samples 3 to 7.6 fold higher than in the parental strain. On the seventh day of cultivation the transformants produced 2 to 5.4 fold more laccase than the parental strain. This indicates that the overexpression of HACA protein induces the production of heterologous proteins in A. niger.