DIRECT OBSERVATION OF THE ROTATION OF F1-ATPASE

Cells employ a variety of linear motors, such as myosin(1-3), kinesin( 4) and RNA polymerase(5), which move along and exert force on a filame ntous structure. But only one rotary motor has been investigated in de tail, the bacterial flagellum(6) (a complex of about 100 protein molec ules(7)). We now show that a single molecule of F-1-ATPase acts as a r otary motor, the smallest known, by direct observation of its motion. A central rotor of radius similar to 1 nm, formed by its gamma-subunit , turns in a stator barrel of radius similar to 5nm formed by three al pha- and three beta-subunits(8). F-1-ATPase, together with the membran e-embedded proton-conducting unit F-0, forms the H+-ATP synthase that reversibly couples transmembrane proton flow to ATP synthesis/hydrolys is in respiring and photosynthetic cells(9,10). It has been suggested that the gamma-subunit of F-1-ATPase rotates within the alpha beta-hex amer(11), a conjecture supported by structural(8), biochemical(12,13) and spectroscopic(14) studies. We attached a fluorescent actin filamen t to the gamma-subunit as a marker, which enabled us to observe this m otion directly. In the presence of ATP, the filament rotated for more than 100 revolutions in an anticlockwise direction when viewed from th e 'membrane' side. The rotary torque produced reached more than 40 pN nm(-1) under high load.