Essential component of the NELF complex, a complex that negatively regulates the elongation of transcription by RNA polymerase II. Has an essential role in postembryonic development. Component of the NELF complex. Associates with polytene chromosomes. Associates with the hsp70 promoter when it is inactive, but not when it is activated. Expressed both maternally and zygotically. Loss of zygotic expression results in morphologically normal embryos that hatch as 1st instar larvae. These larvae survive for several days but do not increase in size. Loss of maternal expression causes arrest prior to the cellular blastoderm stage and embryos display abnormal nuclear morphology. Those that escape this early arrest proceed through the blastoderm stage and gastrulate normally, but then almost always arrest during germband retraction with head defects and incomplete dorsal closure. Belongs to the NELF-A family.