Three covalent attachments anchor heterotrimeric G proteins to cellula
r membranes: the alpha subunits are myristoylated and/or palmitoylated
, whereas the gamma chain is prenylated. Despite the essential role of
these modifications in membrane attachment, it is not clear how they
cooperate to specify G protein localization at the plasma membrane, wh
ere the G protein relays signals from cell surface receptors to intrac
ellular effector molecules. To explore this question, we studied the e
ffects of mutations that prevent myristoylation and/or palmitoylation
of an epitope-labeled alpha subunit, alpha(z). Wild-type alpha(z) (alp
ha(z)-WT) localizes specifically at the plasma membrane. A mutant that
incorporates only myristate is mistargeted to intracellular membranes
, in addition to the plasma membrane, but transduces hormonal signals
as well as does alpha(z)-WT. Removal of the myristoylation site produc
ed a mutant alpha(z) that is located in the cytosol, is not efficientl
y palmitoylated, and does not relay the hormonal signal. Coexpression
of beta gamma with this myristoylation defective mutant transfers it t
o the plasma membrane, promotes its palmitoylation, and enables it to
transmit hormonal signals. Pulse-chase experiments show that the palmi
tate attached to this myristoylation-defective mutant turns over much
more rapidly than does palmitate on alpha(z)-WT, and that the rate of
turnover is further accelerated by receptor activation. In contrast, r
eceptor activation does not increase the slow rate of palmitate turnov
er on alpha(z)-WT. Together these results suggest that myristate and b
eta gamma promote stable association with membranes not only by provid
ing hydrophobicity, but also by stabilizing attachment of palmitate. M
oreover, palmitoylation confers on alpha(z) specific localization at t
he plasma membrane.