The Na-ATPase Gene Is Regulated by the SPS Sensing Pathway and the Stp1/Stp2 Transcription Factors.

The gene, encoding a Na-ATPase, responds transcriptionally to the alkalinization of the medium by means of a network of signals that involves the Rim101, the Snf1 and PKA kinases, and the calcineurin/Crz1 pathways. We show here that the promoter also contains a consensus sequence, located at nt -553/-544, for the Stp1/2 transcription factors, the downstream components of the amino acid sensing SPS pathway. Mutation of this sequence or deletion of either or decreases the activity of a reporter containing this region in response to alkalinization as well as to changes in the amino acid composition in the medium. Expression driven from the entire promoter was affected with similar potency by the deletion of , , or simultaneous deletion of and when cells were exposed to alkaline pH or moderate salt stress. However, it was not altered by the deletion of , encoding the amino acid sensor. In fact, functional mapping of the promoter reveals a region spanning from nt -742 to -577 that enhances transcription, specifically in the absence of Ssy1. We also found that the basal and alkaline pH-induced expression from the , , and, particularly, promoters was notably decreased in an deletion mutant, whereas the and gene reporters were unaffected. Our findings add a further layer of complexity to the regulation of and suggest that the SPS pathway might participate in the regulation of a subset of alkali-inducible genes.