Pol II transcription complex with (ser5) phosphorylated CTD containing extruded transcript to +30 Pol II transcription complex containing extruded transcript to +30 Phosphorylation (Ser5) of RNA pol II CTD Authored: Buratowski, S, 2003-10-15 15:18:41 Phosphorylation of serine 5 residue at the CTD of pol II largest subunit is an important step signaling the end of initiation and escape into processive elongation processes. Cdk7 protein subunit of TFIIH phosphorylates RNA Pol II CTD serine 5 residues on its heptad repeats. Reactome Database ID Release 4377071 Reactome, http://www.reactome.org ReactomeREACT_1185