TCERG1 (transcription elongation regulator 1) is a nuclear transcription factor that couples transcriptional elongation with pre-mRNA splicing. It binds to RNA polymerase II and regulates transcription elongation in a TATA box-dependent manner 1. TCERG1 localizes to both the nucleoplasm and nuclear speckles, where it interacts transiently with both elongation and splicing complexes to coordinate their functions 1. The protein is positioned at the B complex stage of spliceosome assembly 2, and knockdown studies reveal widespread alterations in alternative mRNA processing, including changes to 3'-untranslated regions 3. Mechanistically, TCERG1 exhibits rapid mobility in the nucleus that decreases when associated with active transcription and cotranscriptional splicing sites, suggesting it performs coupling through transient rather than stable interactions 1. Post-translational sumoylation at Lys-503 and Lys-608 negatively regulates its transcriptional activity without affecting splicing function 4. Clinically, TCERG1 is highly expressed in hepatocellular carcinoma and associated with poor prognosis and enhanced cell proliferation, migration, and invasion 5. It is implicated in Huntington's disease pathogenesis, where DNA methylation stabilizes TCERG1-mediated dysregulation of genes controlling enhancer function and transcription elongation 6. TCERG1 depletion impairs neurite outgrowth in neuronal cells, affecting genes involved in cytoskeleton dynamics 7.