The present invention relates to the discovery, identification and characterization of a receptor protein, referred to herein as T1R3, which is expressed in taste receptor cells and associated with the perception of bitter and sweet taste. The invention encompasses transgenic animals and cells that do not express functional T1R3 protein, particularly knock-out animals and cells, and transgenic animals and cells that express a non-native T1R3 protein. Experimental model systems based on these animals and cells can be used to study T1R3-mediated taste transduction and responses of the components of the T1R3 signal transduction pathway to various tastants, furthering our understanding of the molecular biology and biochemistry of taste. Such model systems would also be useful for screening for novel tastants and taste modulators, such as enhancers of desirable flavors, and blockers of undesirable flavors.