pH-regulated expression of the acid and alkaline extracellular proteases of Yarrowia lipolytica

Schools of Biochemistry 1 and Chemical Engineering 2 University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Author for correspondence: Thomas W. Young. Tel: +44 121 414 5437. Fax: +44 121 414 7366. e-mail: t.w.young@bham.ac.uk ABSTRACT Summary: The pH-regulated expression of the acid (AXP) and alkaline (AEP) extracellular proteases of the yeast Yarrowia lipolytica 148 was analysed. Expression in batch and continuous cultures was determined at the mRNA level by Northern blotting, and at the enzyme level by enzyme assays and Western blotting. Culture pH regulated AEP and AXP expression predominantly at the level of mRNA content. Highest levels of AEP mRNA were detected at pH 6.5 whereas highest levels of AXP mRNA were detected at pH 5.5. At pH values either side of these maxima AEP and AXP expression were progressively down-regulated. For both enzymes, the variation in mRNA levels with culture pH occurred progressively rather than by discrete steps. AXP expression did not occur above pH 7.0. Some degree of AEP expression occurred at all pH values tested in two unrelated strains of Y. lipolytica. Keywords: Yarrowia lipolytica , alkaline extracellular protease, acid extracellular protease, pH-regulated expression, mRNA