[Interaction of the beta1-subunit of G-proteins with the actin cytoskeleton]

Using immunoblotting with specific antibodies, we have identified beta 1- and beta 2-subunits of Gi-proteins in membrane and cytosolic fractions of pig lung. It has been shown that beta 1-subunit is present both in membrane and cytosolic fractions, whereas beta 2-subunit is associated only with membranes. Activation of membrane-bound G proteins with non-hydrolysable GTP analogues have led to partial release from membrane of beta 1-, but not beta 2-subunits. When depolymerisation of F-actin during fractionation was prevented, both beta 1- and beta 2-subunits were found in fraction containing total membranes and F-actin. Dialysis of this fraction into low ionic strength buffer caused depolymerization of the bulk of actin and release of about 1/4 of beta 1-subunits into solution. The data presented here suggest that distribution of beta 1-subunits between membrane and cytosol could depend on the state of actin cytoskeleton.