Elongation of RNA polymerase II (Pol II) is thought to be an important mechanism for regulating gene expression . We measured the first wave of de novo transcription in living Drosophila embryos using dual-fluorescence detection of nascent transcripts containing 5' MS2 and 3' PP7 RNA stem loops. Pol II elongation rates of 2.4-3.0 kb/min were observed, approximately twice as fast as earlier estimates [2-6]. The revised rates permit substantial levels of zygotic gene activity prior to the mid-blastula transition. We also provide evidence that variable rates of elongation are not a significant source of differential gene activity, suggesting that transcription initiation and Pol II release are the key determinants of gene control in development.
Keywords: Drosophila embryo; Pol II elongation; live imaging; transcription.
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