Essential component of the NELF complex, a complex that negatively regulates the elongation of transcription by RNA polymerase II by RNA polymerase II. The NELF complex, which acts via an association with the DSIF complex, causes transcriptional pausing. Component of the NELF complex, which is at least composed of TH1/NELF-D and NELF-E. Associates with polytene chromosomes. Associates with the hsp70 promoter when it is inactive, but not when it is activated. The NELF complex possibly dissociates from chromatin following phosphorylation of RNA polymerase II. Belongs to the NELF-D family.