BTF3 (basic transcription factor 3; also nascent polypeptide-associated complex β/NACB) is a member of the NAC-beta family of transcription factors. It is ubiquitously expressed and involved in the initiation of gene transcription by RNA polymerase. BTF3 also appears to impact estrogen receptor alpha (ERα) stimulation of gene activation by binding to both ligand activated and non-ligand activated ERα. Human BTF3 is 206 amino acids (aa) in length and contains one potential phosphorylation site at Ser30, and a NACB domain (aa 82-147). There are multiple potential splice variants. Two variants show alternate start sites, one at Met45 (called BTF3b), and another at Met108.