Nonredundant roles for paralogous proteins in the yeast glucose-sensing pathway

Paralogs engage in biological processes through both redundant and nonredundant functions. In the yeast Saccharomyces cerevisiae, approximately one-fifth of the genome consists of paralogs, with their encoded proteins involved in multiple pathways. However, the unique contributions of individual paralogs have remained poorly defined. Here, we undertook a systematic examination of eight paralog pairs in the glucose-sensing pathways, deleting each component and measuring the resulting changes in gene expression. To that end, we established a new transcription reporter system to monitor the response to glucose as well as to nonpreferred sugars in single cells. Focusing on the PKA catalytic subunits, comprised of the paralogs Tpk1 and Tpk3 as well as the isomorphic kinase Tpk2, we employed mass spectrometry to identify their contribution to cellular metabolism, used a GFP-based sensor to follow changes in cytosolic pH, and used BioID to identify unique and shared candidate binding partners. Our data reveal that paralogs in the glucose-sensing pathway contribute in multiple and unique ways to signal transduction, and establish potential mechanisms driving the preservation of these and other duplicated genes throughout long periods of evolution.