Fig. 1. Live-cell imaging and single-particle tracking of individual mRNPs. Images from time-lapse movies acquired from a cell cotransfected with(A) CFP-lac repressor and (B) YFP-MS2 and induced for more than 30 min. (C) Reduction of noise for tracking of mRNPs was obtained by deconvolution. Bar, 2 µm. (D) Tracking of mRNP particles in a transcriptionally active cell induced for only 20 min (arrow, transcription site) (bar, 2 µm) [Movie S6] showed (E) diffusing particles [Movie S7], (F) corralled particles [Movie S8], (G) stationary particles, and (H) the transcription site. Tracks are marked in green, and time in seconds from the beginning of tracking for eachparticle appears in each frame. Bars, 1 µm. (I) Plot of the area per frame in which each of the tracked particles from this particular cell traveled throughout the tracking period. Diffusive particles are in blue, corralled in green, stationary in yellow, and transcription site in red. Particle 1, particle seen in E; 2, F; 5, G; 6, H. (J) Mean-square displacement (MSD) of tracked nucleoplasmic particles versus time indicated the presence of three types of characterized movements: diffusive (black circles), corralled (blue triangles), and stationary (green squares). Directed movement was never detected (red dotted line; plotted from data of tracked directed cytoplasmic particles). (K) Table summarizing the mean velocities and diffusion coefficients of tracked particles at 37°C. %, percent of tracked particles. D, diffusion coefficient.