The TATA-binding protein-related factors (TRFs) and TATA-binding protein (TBP) are similar in sequence sharing a 180 amino acid saddle-shaped DNA binding core domain. TBP is required by all three RNA polymerases and was considered a universal transcription factor. Subsequently, metazoan TRFs were shown to mediate transcription independently of TBP and to regulate the expression of specific sets of genes. (Adapted from FBrf0162294, FBrf0131150 and FBrf0229757).