# Chapter 21 - Transcriptional Regulation ## Adaptive Quiz - The use of a common set of transcription factors in the regulation of multiple genes is called combinatorial control - Some steroid hormone receptors act as transcriptional activators or repressors, depending on whether they are bound to the hormone - AP-1 heterodimers and homodimers: - combine to regulate diversity of important genes - can activate or repress transcription - are members of the basic leucine-zipper family - can bind with differing affinities to similar promoters