Yeast hEST1A/B (SMG5/6)-like proteins contribute to environment-sensing adaptive gene expression responses

During its natural life cycle, budding yeast (Saccharomyces cerevisiae) has to adapt to drastically changing environments, but how environmental sensing pathways are linked to adaptive gene expression changes remains incompletely understood. Here, we describe two closely related yeast hEST1A-B (SMG5-6)-like proteins termed Esl1 and Esl2 that contain a 14-3-3-like domain and a putative PIN ribonuclease domain. We found that, unlike their metazoan orthologues, Esl1/2 were not involved in nonsense-mediated mRNA decay or telomere maintenance pathways. However, in genome-wide expression array analyses, absence of Esl1 and Esl2 led to >2-fold deregulation of 50 transcripts, most of which were expressed inversely to the appropriate metabolic response to environmental nutrient supply; for instance, normally glucose-repressed genes were de-repressed in esl1Delta esl2Delta double mutants during growth in a high-glucose environment. Likewise, in a genome-wide synthetic gene array screen, esl1Delta esl2Delta double mutants were synthetic sick with null mutations for Rim8 and Dfg16, which form the environmental sensing complex of the Rim101 pH response gene expression pathway. Overall, these results suggest that Esl1 and Esl2 contribute to the regulation of adaptive gene expression responses of environmental sensing pathways.