G protein beta 1 gamma 2 subunits promote microtubule assembly

alpha and beta gamma subunits of G proteins are thought to transduce signals from cell surface receptors to intracellular effector molecules. G(alpha) and G(beta gamma) have also been implicated in cell growth and differentiation, perhaps due to their association with cytoskeletal components. In this report G(beta gamma) is shown to modulate the cytoskeleton by regulation of microtubule assembly, Specificity among beta gamma species exists, as beta 1 gamma 2 stimulates microtubule assembly, and beta 1 gamma 1 is without any effect. Furthermore, a mutant beta 1 gamma 2, beta 1 gamma 2(C68S), which does not undergo prenylation and subsequent carboxyl-terminal processing on the gamma subunit, does not stimulate the formation of microtubules. beta immunoreactivity was detected exclusively in the microtubule fraction after assembly in the presence of beta 1 gamma 2, suggesting a preferential association with microtubules rather than soluble tubulin. Crude microtubule fractions from ovine brain contain G(beta gamma), and electron tron microscopy reveals a specific association with microtubules. The decoration of microtubules by G(beta gamma) appears to be strikingly similar to the periodic pattern observed for microtubule-associated proteins, suggesting a similar site of activation of microtubule assembly by both agents. It is suggested that reformation of the cytoskeleton represents an additional cellular process mediated by G(beta gamma).