The C-terminal domain (CTD) of POLR2A contains about 52 repeats of the consensus heptad YSPTSPS. Serines-2 and 5 of the heptads are phosphorylated in RNA polymerase II initiating transcription of protein coding genes. The exact repeats that are phosphorylated are not known.
Schwinn, DA, Michelotti, GA, Morris, DP
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