Figure 7.

CDK9 is dynamically recruited to transcription factories. FRAP of CDK9-mCherry foci in MEFs. (A) Stills of the live imaging to show the rapid exchange of CDK9. (B) Plot of the average of recovery after bleaching of seven FRAP measurements (±SEM) (AU) Arbitrary units. The real-time movie is shown in Supplemental Movie S5. (C) A model of transcription; gene promoters are loaded with RNAPII-Ser5P (Ser5 light gray) in factories. Elongating RNAPII-Ser2P (Ser2, dark gray) moves to the adjacent nuclear space when it becomes phosphorylated at Ser2 by CDK9. Filled circles represent CDK9, which, together with RNAPII-Ser5P (light gray), is enriched in the factory. CDK9 is also present outside the factory and is exchanged quickly.