Abstract
Signal transduction by G-protein-coupled receptors is regulated by
various mechanisms acting at the receptor level; those studied most
thoroughly are from the beta-adrenergic receptor/Gs/adenylyl cyclase
system. We report here a regulatory mechanism occurring at the level
of the G proteins themselves. A protein with M(r) 33,000 that inhibits
Gs-GTPase activity was purified from bovine brain. This protein is
very similar or identical to phosducin, a protein previously thought
to be specific for retina and pineal gland. Recombinant phosducin
inhibited the GTPase activity of several G proteins, and also inhibited
Gs-mediated adenylyl cyclase activation. Blockade of its inhibitory
effects by protein kinase A suggests that phosducin may be part of
a complex regulatory network controlling G-protein-mediated signalling.
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