PH-REGULATED EXPRESSION OF THE ACID AND ALKALINE EXTRACELLULAR PROTEASES OF YARROWIA-LIPOLYTICA

The pH-regulated expression of the acid (AXP) and alkaline (AEP) extra cellular 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 pred ominantly at the level of mRNA content. Highest levels of AEP mRNA wer e 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 expres sion were progressively down-regulated. For both enzymes, the variatio n in mRNA levels with culture pH occurred progressively rather than by discrete steps. AXP expression did not occur above pH 7.0. Some degre e of AEP expression occurred at all pH values tested in two unrelated strains of Y. lipolytica.