YEAST MITOCHONDRIA CONTAIN ATP-SENSITIVE, REVERSIBLE ACTIN-BINDING ACTIVITY

Sedimentation assays were used to demonstrate and characterize binding of isolated yeast mitochondria to phalloidin-stabilized yeast F-actin . These actin-mitochondrial interactions are ATP sensitive, saturable, reversible, and do not depend upon mitochondrial membrane potential. Protease digestion of mitochondrial outer membrane proteins or saturat ion of myosin-binding sites on F-actin with the S1 subfragment of skel etal myosin block binding. These observations indicate that a protein (or proteins) on the mitochondrial surface mediates ATP-sensitive, rev ersible binding of mitochondria to the lateral surface of microfilamen ts. Actin copurifies with mitochondria during subcellular fractionatio n and is released from the organelle upon treatment with ATP. Thus, ac tin-mitochondrial interactions resembling those observed in vitro may also exist in intact yeast cells. Finally, a yeast mutant bearing a te mperature-sensitive mutation in the actin-encoding ACT1 gene (act1-3) displays temperature-dependent defects in transfer of mitochondria fro m mother cells to newly developed buds during yeast cell mitosis.