G-PROTEIN BETA-1-GAMMA-2 SUBUNITS PROMOTE MICROTUBULE ASSEMBLY

alpha and beta gamma subunits of G proteins are thought to transduce s ignals 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 cytoskeleta l components. In this report G(beta gamma) is shown to modulate the cy toskeleton by regulation of microtubule assembly, Specificity among be ta gamma species exists, as beta 1 gamma 2 stimulates microtubule asse mbly, 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 prenylati on and subsequent carboxyl-terminal processing on the gamma subunit, d oes not stimulate the formation of microtubules. beta immunoreactivity was detected exclusively in the microtubule fraction after assembly i n the presence of beta 1 gamma 2, suggesting a preferential associatio n with microtubules rather than soluble tubulin. Crude microtubule fra ctions from ovine brain contain G(beta gamma), and electron tron micro scopy 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, sug gesting a similar site of activation of microtubule assembly by both a gents. It is suggested that reformation of the cytoskeleton represents an additional cellular process mediated by G(beta gamma).