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. Author manuscript; available in PMC: 2016 May 1.
Published in final edited form as: Trends Biochem Sci. 2015 Apr 13;40(5):257–264. doi: 10.1016/j.tibs.2015.03.005

Figure 3. CTD phosphorylation cycle at UsnRNA genes.

Figure 3

The CTD of RNAPII is first phosphorylated by TFIIH on ser5/7 positions coinciding with transcription initiation and UsnRNA capping. Two possible paths are then taken. This first (left) involves RPAP2 binding to ser7P and dephosphorylation of ser5P. The second scenario (right) involves the binding of a RPRD1A/B dimer to two ser7P, which in turn recruits RPAP2 and positions it to dephosphorylate ser5P. Either of these events is followed by ser2 phosphorylation by p-TEFb leading to the proper dyad modification pattern (ser7P/ser2P) required for Integrator interaction.