Inducible expression of yeast mitochondrial citrate synthase in Aspergillus nidulans.

The coding region of the mitochondrial citrate synthase gene (CIT1) from Saccharomyces cerevisiae was amplified by PCR and cloned into an expression vector (pAL4) downstream of the alcohol dehydrogenase (alcA) promoter of Aspergillus nidulans to yield pALCS1. Transformation of A. nidulans A773 with this construct gave stable transformants, AYC#1 and AYC#2, that were phenotypically stable for several mitotic divisions. Southern blot analysis showed that the CIT1 gene was successfully integrated into the chromosomes of the transformants. Western blot analysis and enzymatic assay for citrate synthase revealed that the integrated yeast gene was subject to inducible expression controlled by alcA promoter, which can be induced by threonine.