Involvement of a G Protein Regulatory Circuit in Alternative Oxidase Production in .

The nuclear gene encodes an alternative oxidase that functions in mitochondria. The enzyme provides a branch from the standard electron transport chain by transferring electrons directly from ubiquinol to oxygen. In standard laboratory strains, is transcribed at very low levels under normal growth conditions. However, if the standard electron transport chain is disrupted, a mRNA expression is induced and the AOD1 protein is produced. We previously identified a strain of , that produces high levels of transcript under non-inducing conditions. Here we have crossed this strain to a standard lab strain and determined the genomic sequences of the parents and several progeny. Analysis of the sequence data and the levels of mRNA in uninduced cultures revealed that a frameshift mutation in the gene results in the high uninduced expression of The gene encodes a regulator of G protein signaling that decreases the activity of the Gα subunit of heterotrimeric G proteins. Our data suggest that strains with a functional gene prevent uninduced expression of by inactivating a G protein signaling pathway, and that this pathway is activated in cells grown under conditions that induce Induced cells with a deletion of the gene encoding the Gα protein still have a partial increase in mRNA levels, suggesting a second pathway for inducing transcription of the gene in We also present evidence that a translational control mechanism prevents production of AOD1 protein in uninduced cultures.