Movie S1. Directed movement of an RNA particle. The movie shows a MS2–GFP-coated RNA particle in the cytoplasm of a cell that has been transfected with a LacZ-MS2 reporter containing the 3’ untranslated region (UTR) of the β-actin gene. The 3’ UTR region is required for the correct localization of the β-actin mRNA to the leading edge of fibroblasts. Reproduced with permission from Fusco et al. Curr. Biol.13, 161-167 (2003).