Figure 2.
DNA-directed RNA polymerase in the three major branches of the tree of life. The bacterial RNA polymerase structure is from T. aquaticus [1iw7]. The eukaryotic RNA polymerase is from S. cerevisiae [1i50]. No structure is available for the archaeal RNA polymerase, but its subunit composition is known to be similar to the eukaryotic enzyme (Bell & Jackson 2001), so it is displayed as a transparent version of the eukaryotic protein complex. The three RNA polymerases exhibit striking structural and functional similarities (Woychik & Reinberg 2001). Structurally and functionally equivalent protein chains are shown in the same colour.