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We have developed a rapid and efficient expression system to study the human β2adrenergic receptor (hu β2AR) in the fission yeast Schizosaccharomyces pombe. This was achieved by cloning the hu β2AR gene, modified by replacement of the 5′ untranslated and a small part of the N-terminal coding sequence (first 14 amino acids) with the corresponding region of the yeast Saccharomyces cerevisiaeSTE2 (α-factor receptor) gene. The gene was then placed under the control of a S. pombeconstitutive promoter for alcohol dehydrogenase (adh). Hu β2AR expression was assessed by immunoblot analysis of the chimeric protein with an anti-STE2 serum raised against a dodecapeptide homologous to the N-terminal amino acids of STE2 and ligand binding was assayed using [ 125I]cyanopindolol. We demonstrate here that the chimeric receptor expressed in S. pombeexhibits the same characteristic ligand specificity and affinity as that of the authentic hu β2AR. This system constitutes a convenient alternative to existing methods for studying seven transmembrane domain receptors due to its simplicity and high reproducibility.

The effect of peptides homologous to segments of a G protein‐coupled receptor on the GTPase activity of recombinant G0α (rGoα) and G,a (rGsα) has been tested. These peptides contain overlapping sequences spanning from amino acid 212 of the putative fifth transmembrane domain to amino acid 229 of the third cytoplasmic loop of the a2 adrenergic receptor. Interestingly, two peptides (comprising residues 212–227 and 214–227) strongly inhibit the basal GTPase activity of both rGoα and rGsα. Instead, a C‐terminally extended peptide (residues 216–229) stimulates rGoα but slightly inhibits rGsα. Circular dichroism spectroscopy of the peptides reveals that an a helical structure is more easily inducible in the inhibitory ones. These findings constitute an example of peptides representing cytoplasmic receptor sequences that differentially modulate the GTPase activity of recombinant G protein α‐subunits.