Figure 1. Subunit complexity of RNA polymerases. The sizes of the subunits are approximate; the diagram is a generalization and is not intended to accurately display precise subunit interactions or enzyme structure.

Figure 2. Reconstitution of selective transcription assays with RNA polymerases I, II, and III. The three types of RNA polymerases are shown with the respective protein fractions required to achieve promoter-selective transcription in vitro. Many of the activities represented in the protein fractions contain multiple polypeptides. Alternate names are shown in parentheses.

Figure 3. Evolutionary conservation of RNA polymerase. Relative subunit sizes are approximate; Saccharomyces cerevisiae represents eukaryotic RNA polymerase subunit structure, Escherichia coli represents bacterial subunit structure and Sulfolobus (Sulfolobus acidocaldarius) represents archaebacterial subunit structure.

Figure 4. Nuclear RNA polymerases are structurally and functionally similar. Subunits of yeast Saccharomyces cerevisiae are used as an example.

Figure 5. C-terminal domain (CTD) length and sequence in RNA polymerase II. Each open box represents one CTD heptapeptide, the black rectangles (not drawn to scale) represent RNA polymerase II large subunit amino acids in front of the CTD. The sequence of the Saccharomyces cerevisiae CTD (bold-faced residues display deviation from the canonical consensus sequence) from a commonly used laboratory strain is shown. The yeast CTD shows strain variability, comprising either 26 or 27 repeats.

Figure 6. RNA polymerase II structure. Saccharomyces cerevisiae RNA polymerase II/4/7 structure. The position of the 25 Å DNA-binding cleft is indicated (white asterisk), and individual subunits are represented in different colours. Figure courtesy of Richard H. Ebright, HHMI and Rutgers University.