Source:http://linkedlifedata.com/resource/umls/id/C3158210
GO: Interacting selectively and non-covalently with any protein or protein complex (a complex of two or more proteins that may include other nonprotein molecules), in order to modulate transcription. A protein binding transcription factor may or may not also interact with the template nucleic acid (either DNA or RNA) as well. [GOC:txnOH]