In the yeast Saccharomyces cerevisiae, glucose signals activate the production of cellular cAMP. This signaling pathway is called the cAMP-protein kinase A (PKA) pathway, which plays a major role in the regulation of cell growth, metabolism, and stress resistance. Extensive studies have been carried out to clarify the mechanism of this pathway, and many factors involved in the pathway have been identified such as small G proteins, the GDP-GTP exchange factor, adenylate cyclase, and PKA. Also, additional elements involved in this pathway have been evaluated in the last decade. A heterotrimeric G protein alpha subunit was identified as a mammalian G alpha homologue, and a G-protein-coupled receptor (GPCR), which initiates the signaling pathway in response to glucose addition, was identified. GPCR-G alpha was shown to function in a signaling pathway that acts parallel to small G proteins. These signaling pathways regulate cell growth and differentiation in response to nutrients.