ACTIN-FILAMENT MOTION IN THE IN-VITRO MOTILITY ASSAY HAS A PERIODIC COMPONENT

The interaction between actin and myosin can be studied in the in vitr o motility assay, where fluorescently labelled actin filaments are obs erved to move over a lawn of myosin heads. To examine details of this movement, we measured systematically the velocities of the front end, rear end, and centroid of the actin filament as the filament translate d over the assay surface. We found that these velocities exhibited an unexpectedly periodic component, alternating regularly between high an d low values, superimposed on the steady velocity component. The perio d of the oscillatory component was approximately 380 ms. When translat ion was stopped by an increase in osmolarity, the filaments wiggled wi th a periodicity similar to the translating filament, implying that wi ggling and translation may be related. Rigor filaments showed no perio dicity. From the frequency content of the auto-and cross-correlation f unctions derived from the velocities of the front end, rear end, and c entroid of the actin filament, we infer a deterministic, possibly wave -like process travelling along the actin filament. Potential molecular mechanisms underlying this phenomenon are considered. (C) 1997 Wiley- Liss, Inc.