Characterization of an inducible expression system in Aspergillus nidulans using alcA and tubulincoding genes

Plasmids have been constructed in which expression of agene can be placed under the control of the inducible promoter of the alcA gene encoding alcohol dehydrogenase I in Aspergillus nidulans. Simplified shuttle vectors carrying pyr4 which complements pyrG89 mutations have also been constructed. These are based on pUC19 and retain α-peptide expression. The β-tubulin genes, tube and benA, have been placed under the control of alcA and their expression studied. Levels of expression can be assayed phenotypically because increased synthesis of β-tubulin inhibits vegetative growth. Sensitivity of asexual spore formation to the anti-microtubule drug benomyl provides a means of detecting very low levels of expression of the chimeric genes. Glucose almost completely represses the chimeric genes. Induction is rapid and is maximal within an hour. When a strain carrying seven copies of an alcA :: tubC gene fusion was grown under inducing conditions, 6.5% of total sulfate labelled protein consisted of tubC product. Cyclopentanone was the most potent inducer of the chimeric genes on solid media but it also partially inhibited growth. Chimeric alcA :: tubC and alcA :: benA genes were expressed to very similar levels despite the fact that tubC utilizes many rare codons.