Abstract
The genome of the methylotrophic yeast, Komagataella phaffii harbours multiple genes encoding putative alcohol dehydrogenases and aldehyde dehydrogenases (ALDs). Here, we demonstrate that one of the ALDs denoted as ALD-A is essential for ethanol metabolism. A zinc finger transcription factor known as Mxr1p regulates ALD-A transcription by binding to Mxr1p response elements (MXREs) in the ALD-A promoter. Mutations which abrogate Mxr1p binding to ALD-A MXREs in vitro abolish transcriptional activation from ALD-A promoter in vivo. Mxr1p regulates ALD-A expression during ethanol as well as methanol metabolism. ALD-A is essential for the utilization of methanol and Δald-a is deficient in alcohol oxidase (AOX), a key enzyme of methanol metabolism. AOX protein but not mRNA levels are down regulated in Δald-a. ALD-A and AOX localize to cytosol and peroxisomes respectively during methanol metabolism suggesting that they are unlikely interact with each other in vivo. This study has led to the identification of Mxr1p as a key regulator of ALD-A transcription during ethanol and methanol metabolism of K. phaffii. Post-transcriptional regulation of AOX protein levels by ALD-A during methanol metabolism is another unique feature of this study.
