FIGURE 1.

A representative example of bacterial movement in Xenopus egg cytoplasmic extract. (A) False-color map of GFP (blue) and rhodamine-actin (red) fluorescence signals in the 100th frame of a 250-frame movie, with derived bacterial path over all frames in the movie superimposed with hash marks positioned at 2-s intervals (black). Inset shows entire frame visible to microscope with several tracked paths. Each point indicates position of bacterial centroid (dot) and orientation of long axis of the bacterium (perpendicular line). (B) Instantaneous fluorescence cross-sections along the path of the bacterium, for the 100th frame. Each cross-section is centered on the bacterium and oriented perpendicular to the direction of motion at that point, generating a computationally straightened actin comet tail. (C) Integrated fluorescence across GFP (blue) and rhodamine-actin (red) cross-sections, for the image shown in B. (D) Point-by-point estimated instantaneous speed as a function of time throughout the recording.