The present invention pertains to novel yeast cells which are useful for the expression of heterologous G protein coupled receptors. The yeast cells of the present invention can be used in screening assays which can be used to screen for modulators of G protein coupled receptors. Specifically, the invention provides novel yeast cells which express a heterologous G protein coupled receptor and mutant and/or chimeric G protein subunit molecules which serve to functionally integrate the heterologous into the pheromone signaling pathway of the yeast cell. The invention also provides for the expression of heterologous G protein coupled receptors which are functionally integrated into the yeast cell membrane using a yeast .alpha. factor leader sequence. Drug discovery assays using the subject yeast cells are also provided.