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(Nature Structural and Molecular Biology 2014, 21:686-95). Human RNA polymerase II carboxyl-terminal domain (CTD) contains 52 heptapeptide repeats that are important for transcriptional regulation and transcription-coupled RNA processing.  This work demonstrates that dimeric RPRD proteins specifically recognize serine 2 and serine 7 phosphorylated (S2P, S7P) CTD repeats so as to organize the CTD into “CTDsomes” and recruit the phosphatase RPAP2 for CTD serine 5 (S5P) dephosphorylation.