THE ALPHA-SUBUNITS OF G-PROTEINS G(12) AND G(13) ARE PALMITOYLATED, BUT NOT AMIDICALLY MYRISTOYLATED

The alpha-subunits of the G-proteins G(12) and G(13) were expressed with a baculovirus system in insect cells and analysed for acylation. Both proteins incorporated tritiated palmitic and to a lesser extent also tritiated myristic acid. Radiolabel from both fatty acids was sensitive to treatment with neutral hydroxylamine. This result supports a thioester-type fatty acid bond and argues against amidical N-myristoylation. Fatty acid analysis after labeling with [H-3]palmitic acid showed that palmitate represents the predominant fatty acid linked to G alpha(12) and G alpha(13). Separation of cells into cytosolic and membranous fractions revealed that palmitoylated alpha-subunits of G12 were exclusively membrane-bound, whereas [S-35]methionine-labeled proteins were detected in soluble and particulate fractions. Inhibition of protein synthesis with cycloheximide did not block palmitoylation of the alpha-subunits, which indicates that palmitoylation occurs independently of protein synthesis.