Essential component of the NELF complex, a complex that negatively regulates the elongation of transcription by RNA polymerase II (PubMed:10199401). The NELF complex, which acts via an association with the DSIF complex and causes transcriptional pausing, is counteracted by the P-TEFb kinase complex (PubMed:11940650, PubMed:12612062). Provides the strongest RNA binding activity of the NELF complex and may initially recruit the NELF complex to RNA (PubMed:18303858, PubMed:27282391). (Microbial infection) The NELF complex is involved in HIV-1 latency possibly involving recruitment of PCF11 to paused RNA polymerase II. The NELF complex is composed of NELFA, NELFB, NELFCD (isoform NELF-C or isoform NELF-D) and NELFE (PubMed:10199401, PubMed:27282391). Interacts with NELFB (By similarity). (Microbial infection) Binds to the HIV-1 TAR RNA which is located in the long terminal repeat (LTR) of HIV-1. Localizes to chromatin (PubMed:14701750). Phosphorylation by the P-TEFb complex promotes its release from chromatin (PubMed:14701750). Widely expressed. Expressed in heart, brain, lung, placenta, liver, skeletal muscle, kidney and pancreas. The RRM domain interacts with RNA, and is essential for NELF complex function. It is however not required for the NELF complex formation. Phosphorylated by the P-TEFb complex at sites next to its RNA recognition motif, promoting its release from chromatin. Sumoylated. Belongs to the RRM NELF-E family.