NELFB is a subunit of negative elongation factor (NELF), which also includes NELFA (WHSC2; MIM 606026), either NELFC or NELFD (TH1L; MIM 605297), and NELFE (RDBP; MIM 154040). NELF acts with DRB sensitivity-inducing factor (DSIF), a heterodimer of SPT4 (SUPT4H1; MIM 603555) and SPT5 (SUPT5H; MIM 602102), to cause transcriptional pausing of RNA polymerase II (see MIM 180660) (Narita et al., 2003 [PubMed 12612062]).