G protein-coupled receptors (GPRs) are a protein family of transmembrane receptors that transmit an extracellular signal (ligand binding) into an intracellular signal (G protein activation). GPR signaling is an evolutionarily ancient mechanism used by all eukaryotes to sense environmental stimuli and mediate cell-cell communication. All of the receptors have seven membrane-spanning domains and the extracellular parts of the receptor can be glycosylated. These extracellular loops also contain two highly conserved cysteine residues which create disulfide bonds to stabilize the receptor structure. Gpr1 is required for yeast-to-hypha transition on various solid hypha-inducing media, and important for yeast cell morphology. It activates guanine nucleotide exchange on Gpa2 which stimulates cAMP synthesis by glucose. In Saccharomyces cerevisiae, Gpr1 is necessary for filamentous and invasive growth.