Fig. 6. Heterotrimer formation at the plant plasma membrane requires dual lipidation of G and G. The model shows the formation of Gß dimers in the cytosol. The waste-basket symbolizes the breakdown of Gß that occurs in the absence of G. Dimerization does not require lipidation. Dual lipidation of G targets the Gß dimer to the plasma membrane where it can form a heterotrimer with G that has been myristoylated in the cytosol and palmitoylated, probably at the plasma membrane. The heterotrimer does not fall apart upon activation of G (^*). The arrows indicate the putative direction(s) of the reactions. Heterodimer and heterotrimer formation might be regulated by de/repalmitoylation cycles.