Cell Biology

Hitching a Ride

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Science  20 Sep 2002:
Vol. 297, Issue 5589, pp. 1959-1961
DOI: 10.1126/science.297.5589.1959e

Heterotrimeric G proteins function in multiple signalling pathways at the plasma membrane; however, their intracellular itinerary to achieve their correct localization at the cytoplasmic face of the plasma membrane is not clear. Michaelson et al. examined the synthesis and transport of fluorescently tagged G-protein α and γ subunits in living cells. The Gγ subunit and Gβ subunit form a dimer soon after synthesis in the cytosol and are trafficked together through the cell. Soon after synthesis, the Gγ subunit acquires a lipid modification. The Gγ subunit also contains a CAAX motif that targets the dimer to the cytoplasmic face of the endoplasmic reticulum, where AAX is cleaved and the subunit is carboxymethylated. The processed dimer is then transported to the Golgi complex and then needs to assemble with the Gα subunit, which is also lipid-modified, before transport along the secretory pathway to the plasma membrane. The requirement for two separate targeting signals—CAAX processing and heterotrimerization—to allow correct localization of the heterotrimer is analogous to the dual-signal plasma membrane targeting observed in another family of signalling proteins, the Ras proteins. — SMH

MBC in Press 10.1091/mbc.E02-02-0095 (2002).

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