Functional domains of the Gs alpha subunit: role of the C-terminus in the receptor-dependent and receptor-independent activation.

We have developed a rapid and simple model for studying functional domains of Gs alpha subunit, the GTP binding protein involved in adenylyl cyclase activation. Cyc- membranes prepared from a variant S49 cell line which does not express the alpha subunit of Gs are reconstituted by the in vitro translated Gs alpha subunit. Since the messenger RNA used for in vitro translation is generated from in vitro transcription of the cDNA encoding Gs alpha subunit, it is possible to introduce genetic modifications at the nucleotide level and analyze their consequences at the amino-acid level on the functional properties of the protein. We have constructed mutated alpha chains which correspond to various deletions of the carboxy-terminal region. Removal of the 9 carboxy-terminal residues uncoupled the alpha subunit from the receptor whereas deletion of the 26 carboxy-terminal residues blocked any activation induced either in a receptor-dependent or in a receptor-independent manner.