Mapping of subunit-subunit contact surfaces on the beta' subunit of Escherichia coli RNA polymerase.

The RNA polymerase core enzyme of Escherichia coli with the catalytic activity of RNA polymerization is assembled sequentially under the order: 2alpha --> alpha(2) --> alpha(2)beta --> alpha(2)betabeta'. The core enzyme gains the activities of promoter recognition and transcription initiation after binding the sigma subunit. The subunit-subunit contact surfaces of beta' subunit (1407 residues) were analyzed by testing complex formation between various beta' fragments and either the alpha(2)beta complex or the sigma(70) subunit. Results indicate that two regions, one central region between residues 515 and 842 and the other COOH-terminal proximal region downstream from residue 1141, are involved in binding the alpha(2)beta complex; and the NH(2)-terminal proximal region between residues 201 and 345 plays a major role in binding the sigma(70) subunit. However, both alpha(2)beta binding sites have weak activity of the sigma(70) subunit; likewise, the sigma(70) subunit-contact surface has weak binding activity of the alpha(2)beta complex. The sites involved in the catalytic function of RNA polymerization are all located within two spacer regions sandwiched between these three subunit-subunit contact surfaces.