(A) Movements of LacZ-24-ßact mRNAs. Cos cell transiently cotransfected with pMS2-GFP and pRSV-Z-24-ßact, imaged live. Left: a maximum intensity image projection of 200 frames. The scale bar represents 10 µm. Right: panel magnifications: track of mRNA movement superimposed (green) on an enlargement from each of the indicated boxed regions. The scale bar represents 2 µm. (See Movies 3 and 4 in the Supplementary Material).

(B) Influence of a zipcode sequence on moving particles. Moving particles of GFP-labeled RNA, observed in the image sequences acquired, were classified as either directed, diffusional, corralled, or static. The average distribution from cells transfected with an mRNA reporter either containing (LacZ-24-ßact) or not containing (LacZ-24-hGH, LacZ-24-SV) the ß-actin zipcode sequence are shown. (n = 9 image sequences each, 162 particles. The bars report the standard errors).

(C and D) Colocalization of directed motion with microtubules. (C) Cos cells transiently cotransfected with pMS2-YFP, pCFP-tubulin, and pRSV-Z-24-ßact, imaged live. Left: maximum intensity image projection of YFP; right, CFP. The scale bar represents 10 µm. (D) Merged images of CFP microtubules (red) with sequences of movement of the RNA labeled with MS2-YFP (green). The scale bar represents 2 µm. The arrowheads point to the particle center of mass at t = 0 and t = 2.67 s. The distance between the arrowheads is 2.7 µm (particle speed = 990 nm/s).