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 activ ity of RNA polymerization is assembled sequentially under the order: 2 alph a-->alpha(2)-->alpha(2)beta-->alpha(2)beta beta'. The core enzyme gains the activities of promoter recognition and transcription initiation after bind ing the sigma subunit, The subunit-subunit contact surfaces of beta' subuni t (1407 residues) were analyzed by testing complex formation between variou s beta' fragments and either the alpha(2)beta complex or the sigma(70) subu nit. Results indicate that two regions, one central region between residues 515 and 842 and the other COOH-terminal proximal region downstream from re sidue 1141, are involved in binding the alpha(2)beta complex; and the NH2-t erminal proximal region between residues 201 and 345 plays a major role in binding the sigma(70) subunit. However, both alpha(2)beta binding sites hav e weak activity of the sigma(70) subunit; likewise, the sigma(70) subunit-c ontact surface has weak binding activity of the alpha(2)beta complex. The s ites involved in the catalytic function of RNA polymerization are all locat ed within two spacer regions sandwiched between these three subunit-subunit contact surfaces.