Acts as a transcriptional repressor for zinc finger transcription factors EGR1 and EGR2. Isoform 2 lacks repression ability. Homomultimers may associate with EGR1 bound to DNA. Isoform 2 is not localized to the nucleus. Highly expressed in brain and thymus, and at lower levels in spleen, kidney, heart and testis. Isoform 1 is predominantly expressed in testis, whereas isoform 3 is more abundant in thymus. By serum stimulation. The NAB conserved domain 1 (NCD1) interacts with EGR1 inhibitory domain and mediates multimerization. The NAB conserved domain 2 (NCD2) is necessary for transcriptional repression. Sumoylation by EGR2 represses EGR2 transcriptional activity in hindbrain. Belongs to the NAB family.