INTERACTION OF TUBULIN WITH THE PLASMA-MEMBRANE - TUBULIN IS PRESENT IN PURIFIED PLASMALEMMA AND BEHAVES AS AN INTEGRAL MEMBRANE-PROTEIN

Using monoclonal antibodies we have studied the interaction of tubulin with the plasma membrane of leaves of Nicotiana sylvestris (Speg. et Comes) and tobacco suspension-culture cells. The results show that iso lated plasma membranes contain tightly bound alpha-tubulins. Their ass ociation with the plasma membrane is resistent to non-ionic detergent and to low and high ionic strength. Only extraction with sodium dodecy l sulfate is capable of dissociating these cytoskeletal proteins. It i s unlikely that this membrane-bound tubulin is present in its polymeri c form because electron-microscopical analysis does not reveal the pre sence of filaments, whereas treatment of membranes with oryzalin (whic h has been shown to destabilize microtubules in vitro) does not remove the tubulins from isolated plasma membrane. When living cells are tre ated with oryzalin, the amount of membrane-associated tubulin is drast ically reduced, which could mean that its presence is related to in-vi vo microtubule dynamics.