The authors developed a method for immunoaffinity purification of Saccharomyces cerevisiae adenylyl cyclase using a fusion protein with a small peptide epitope. They constructed a plasmid that expressed the fusion protein from the S. cerevisiae alcohol dehydrogenase promoter ADH1. A monoclonal antibody directed against the peptide was used to purify the adenylyl cyclase by affinity chromatography. The purified enzyme appeared to be a multisubunit complex consisting of a 200-kilodalton adenylyl cyclase fusion protein and an unidentified 70-kilodalton protein. The purified protein could be activated by RAS proteins, with activation requiring a guanine nucleoside triphosphate (GTP). The study aimed to understand the interaction between RAS and adenylyl cyclase in yeast, providing insights into signal transduction pathways.The authors developed a method for immunoaffinity purification of Saccharomyces cerevisiae adenylyl cyclase using a fusion protein with a small peptide epitope. They constructed a plasmid that expressed the fusion protein from the S. cerevisiae alcohol dehydrogenase promoter ADH1. A monoclonal antibody directed against the peptide was used to purify the adenylyl cyclase by affinity chromatography. The purified enzyme appeared to be a multisubunit complex consisting of a 200-kilodalton adenylyl cyclase fusion protein and an unidentified 70-kilodalton protein. The purified protein could be activated by RAS proteins, with activation requiring a guanine nucleoside triphosphate (GTP). The study aimed to understand the interaction between RAS and adenylyl cyclase in yeast, providing insights into signal transduction pathways.