Representative traces from rhodamine-labeled actin filaments twirling over myoV-6IQ (left) or myoV-4IQ (right). Measured intensities (A and B): The total measured intensity is shown (A), along with its 16 component intensities (B). The rhodamine probe bleached when the intensities dropped to baseline. (C–E) Calculation of the orientation of the probe in the actin frame of reference: Traces of the angles δ_P (C), β_P (D), and α_P (E) in the actin frame. Note that α_P declines linearly for myoV-6IQ, indicating left-handed twirling, and that α_P increases linearly for myoV-4IQ, indicating right-handed twirling in this particular molecule.