NELFB is a subunit of the negative elongation factor (NELF) complex that regulates RNA polymerase II transcription elongation. (a) Primary function: NELFB participates in promoter-proximal pausing of RNA polymerase II, acting as a transcriptional brake that can be released for productive elongation 1. The NELF complex, including NELFB, stabilizes paused polymerase at promoters and enhancers 2. (b) Mechanism: NELF functions by binding to paused RNA polymerase II-DSIF complexes and must be displaced by factors like PAF complex for pause release and elongation activation 1. Under stress conditions, NELF rapidly forms nuclear condensates through dephosphorylation and SUMOylation, facilitating enhanced recruitment to promoters for coordinated transcriptional downregulation 3. (c) Disease relevance: NELF plays roles in cancer progression, with NELF-E (complex partner) involved in breast cancer through regulation of epithelial-mesenchymal transition and stemness genes 4. The complex is also implicated in HIV-1 latency through interactions with viral regulatory elements 5. (d) Clinical significance: NELF condensation is required for cellular viability under stress 3, and targeting transcriptional elongation control shows therapeutic potential in inflammatory diseases 6.