Negative elongation factor B (NELF-B), also known as Cofactor of BRCA1 (COBRA1), is a protein which in humans is encoded by the NELFB gene.
NELF-B is a subunit of negative elongation factor (NELF), which also includes NELF-A, either NELF-C or NELF-D (NELF-C/D), and NELF-E. NELF acts with DRB sensitivity-inducing factor (DSIF), a heterodimer of SPT4 (SUPT4H1) and SPT5 (SUPT5H), to cause transcriptional pausing of RNA polymerase II. COBRA1 was initially identified in a yeast two-hybrid screen using the BRCT1 domain of BRCA1 as bait.
NELF-B has been shown to interact with: