Expression of the Four Subunits of the Torpedo Californica Nicotinic Acetylcholine Receptor in Saccharomyces cerevisiae

Yeast expression vectors were constructed containing complementary DNA encoding the α-, β-, γ-, and δ-subunits of the Torpedo californica nicotinic acetylcholine receptor under the control of the Saccharomyces cerevisiae alcohol dehydrogenase promoter. All four plasmids were integrated into the yeast genome of a single yeast cell. The resulting yeast strain synthesized polypeptides novel to yeast that had the molecular weights and antigenic properties similar to the authentic T. californica receptor α-, γ, and δ-subunits. The β-subunit polypeptide could not be detected in this yeast strain, even though the poly(A)+ RNA from this strain contained all the information necessary for the expression of functional acetylcholine receptors in Xenopus laevis oocytes. The replacement of the β-subunit mRNA 5′-untranslated leader and its N-terminal signal sequence by the corresponding α-subunit sequences, however, resulted in the expression of the β-subunit polypeptide in yeast grown at 5 °C.