Mapping of the Rsd contact site on the sigma 70 subunit of Escherichia coli RNA polymerase

Rsd (regulator of sigma D) is an anti-sigma factor for the Escherichia coli RNA polymerase sigma (70) subunit. The contact site of Rsd on sigma (70) w as analyzed after mapping of the contact-dependent cleavage sites by Rsd-te thered iron-p-bromoacetamidobenzyl EDTA and by analysis of the complex form ation between Ala-substituted sigma (70) and Rsd. Results indicate that the Rsd contact site is located downstream of the promoter -35 recognition hel ix-turn-helix motif within region 4, overlapping with the regions involved in interaction with both core enzyme and sigma (70) contact transcription f actors.