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Transcription elongation is the stage of RNA synthesis in which an RNA polymerase, assembled in a stable elongation complex with a DNA template and nascent RNA, moves along the template strand and sequentially incorporates ribonucleoside triphosphates into the 3′ end of the RNA molecule. Catalysis proceeds through template-directed base pairing, phosphodiester-bond formation at the polymerase active center, translocation of the enzyme–nucleic-acid complex, and displacement of the growing RNA transcript from the DNA–RNA hybrid ^[1][2]. The elongation complex maintains processive RNA synthesis while undergoing conformational changes and responding to sequence-encoded pause signals, DNA topology, chromatin or nucleoprotein structure, and associated elongation factors. In eukaryotic RNA polymerase II systems, phosphorylation of the C-terminal domain and recruitment of co-transcriptional RNA-processing and chromatin-associated factors form integral features of productive elongation ^[3].