Movie S1.

Transfer of β-actin–MBS mRNA between donor and acceptor MEFs. Acceptor WT MEFs and donor β-actin–MBS MEFs expressing tdMCP–GFP were cocultured for 2.5 h and imaged with a 150× objective, as detailed in Materials and Methods. Both cell types express TagRFP-T-ps. Cells were imaged at 7-s intervals, eight z-sections of 0.6-µm each, for 14 min. Exposure time for each wavelength was 100 ms (488-nm laser at 20% power, 561-nm laser at 20% power). Green, GFP; magenta, TagRFP-T. The movie shows maximum projection of 61 frames at 5 fps (total elapsed time = ∼7 min, starting from frame no. 30) of the upper two z-sections. (Scale bar: 5 µm.) Note the linear progress of the β-actin–MBS mRNA spot between donor and acceptor MEFs.