The α subunits of Gs and Gi link different sets of hormone receptors to stimulation and inhibition, respectively, of adenylyl cyclase. A chimeric αi/αs cDNA was constructed that encodes a polypeptide composed ofthe amino terminal 60% of an αi chain and the carboxyl terminal 40% of αs. The cDNA was introduced via a retroviral vector into S49 cyc- cells, which lack endogenous αs. Although less than half of the hybrid α chain is derived from αs, its ability to mediate β-adrenoceptor stimulation of adenylyl cyclase matched that of the normal αs polypeptide expressed from the same retroviral vector in cyc- cells. This result indicates that carboxyl terminal amino acid sequences of αs contain the structural features that are required for specificity of interactions with the effector enzyme, adenylyl cyclase, as well as with the hormone receptor.
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