Movie S3. Visualizing gene expression in living cells. The movie shows a cell with a stably integrated gene that also contains 256 lac operator repeats. This gene transcribes an RNA that contains both a coding sequence for the cyan fluorescent protein (CFP) protein (with a peroxisome-targeting sequence) and a stretch of MS2 stem-loops. In the beginning of the movie, the gene locus is visible as a result of tagging of the DNA with a CFP–lac-repressor protein. Once transcription is induced from this gene, the locus becomes structurally open and decondenses. The RNAs produced from the gene are tagged with yellow fluorescent protein (YFP)–MS2 and can be seen accumulating at the transcription site. The RNA is translated in the cytoplasm and at later times post-induction, CFP-labelled peroxisomes are detected. The cell was imaged every 2.5 min for a total of 4 hr and 22.5 min. Reproduced with permission from Janicki et al. Cell 116, 683-698 (2004).