tokens: Basal components of the transcription apparatus ( RNA polymerase II , TATA - binding protein ) contain activation domains : is the repetitive C - terminal domain ( CTD ) of RNA polymerase II a " portable enhancer domain " ? Regions rich in serine , threonine , and proline residues can be found in transcriptional activation domains , as well as in the N - terminal parts of mammalian TATA - binding proteins , where they are interrupted by polyglutamine stretches .