NELF-A (negative elongation factor A), NELF-B, NELF-C, NELF-D and NELF-E are components of the NELF complex, which is a a structure that negatively regulates Pol II-dependent transcription elongation. Control of transcription elongation requires a complex interplay between positive transcription elongation factor b (P-TEFb) and negative transcription elongation factors, DSIF and NELF. DSIF and NELF, act as negative transcription elongation factors by increasing the time the polymerase spends at pause sites. DSIF/NELF inhibition of transcription is prevented by P-TEFb in cooperation with FACT.