Figure 1. Evolutionary conservation of ribonucleic acid polymerases (RNAPs). Relative subunit sizes are approximate; ‘human’ represents all metazoan RNAP subunits, yeast (S. cerevisiae) represents lower eukaryotic RNAP subunits. The bacterial subunit composition represents that used under normal culture conditions. The eukaryotic subunit nomenclature originated from yeast RNAP.

Figure 2. RNA polymerase II C-terminal domain (CTD). Each square box represents one CTD heptapeptide; the filled rectangles (not drawn to scale) represent RNAP II large subunit amino acids in front of the CTD. The consensus sequence shown represents the most prevalent repeated sequence in the overall CTD. A one- or two-amino-acid deviation from the consensus sequence is also common. The length of the yeast CTD shows strain variability: it can comprise either 26 or 27 repeats.

Figure 3. RNAP II transcription machinery. All sizes are approximate. Subunit and transcription factor placement in the respective complexes is not intended to reflect known interactions. Adapted from Woychik and Hampsey (2002).

Figure 4. Yeast and human Mediator complexes. Subunits of yeast Mediator are grouped and listed by name, not by apparent molecular weight. The example used for human Mediator is the Srb- and Med-containing cofactor complex–thyroid receptor-associated protein complex (SMCC/TRAP); subunit names reflect apparent molecular weight. Evolutionary conservation exists between twelve subunits in the two complexes; each related pair is linked by a line (subunit similarities adapted from Malik and Roeder 2000; Boube et al. 2002).