The highly efficient Semliki Forest virus (SFV) system has been applied to express several recombinant 7TM receptors and ligand-gated ion channels. High affinity binding and functional coupling to G proteins were obtained for the receptors. The ligand-gated ion channels showed high specific binding activity and high-amplitude electrophysiol. responses in whole-cell patch clamp recordings. The rapid and simple generation of high titer virus stocks has made the SFV system also useful for site-directed mutagenesis studies. The broad host range of SFV has allowed studies of recombinant proteins in a wide variety of cell lines and primary cell cultures. Scale-up technol. for SFV has been established. Recombinant SFV particles contg. a his-tagged mouse serotonin 5-HT3 receptor gene were used to infect suspension cultures of BHK cells at reactor scale (11.5 L). Receptor yields of 15 mg (Bmax values of 52 pmol mg-1) were obtained. The receptor was solubilized, isolated to high purity and subjected to structure-function studies. [on SciFinder (R)]