Structure and Function in Promoter Escape by T7 RNA Polymerase
T7 RNA polymerase is an ideal model system in which to study fundamental characteristics of the complex machine that is RNA polymerase. Although structurally unrelated to the more complex multi‐subunit RNA polymerases, it appears that the common functional requirements imposed on all DNA dependent RNA polymerases is likely to be reflected in many common mechanistic features. Both the small size of the protein and the small size of the promoter DNA allow studies in the single subunit enzymes which are difficult or impossible in the much larger multi‐subunit enzymes. Similarly, the ability to prepare large amounts (and concentrations) of highly active T7 RNA polymerase opens doors that remain largely shut to the multi‐subunit systems. A self‐consistent picture of the critical transition from initiation to elongation is beginning to emerge. The resulting model presented here generates new testable hypotheses that will allow us to further refine our understanding of this complex molecular machine.