ROLE OF THE ACTIN CYTOSKELETON IN REGULATING THE OUTER PHOSPHATIDYLETHANOLAMINE LEVELS IN YEAST PLASMA-MEMBRANE

Transbilayer phosphatidylethanolamine (PtdEtn) movements in the plasma membrane of Saccharomyces cerevisiae are regulated by an ATP-dependen t, protein-mediated process(es). To examine whether this process is in fluenced by the actin cytoskeleton, we have studied the PtdEtn translo cation in S. cerevisiae cells after treatment with microfilament disru pting and microtubule-disrupting agents. PtdEtn translocation was stud ied by measuring the external PtdEtn levels, using fluorescamine as th e external membrane probe, in the ATP-depleted, ATP-depleted and reple ted, and N-ethylmaleimide-treated cells. The microfilaments and microt ubules were disrupted by treatment with various cytochalasins and colc hicine (or benomyl) respectively PtdEtn translocation became abnormal in the cytochalasin-treated cells but not in cells that were treated w ith microtubule-disrupting agents, such as colchicine or benomyl. Thes e results have been interpreted to suggest that the actin cytoskeleton is involved in regulating the PtdEtn translocase activity in the yeas t cell plasma membrane.