21097628
not annotated - annotated - LINNAEUS only
Promoter discrimination at class I MarA regulon promoters mediated by glutamic acid 89 of the MarA transcriptional activator of Escherichia coli.
Three paralogous transcriptional activators MarA, SoxS, and Rob, activate > 40 Escherichia coli promoters. To understand why MarA does not activate certain promoters as strongly as SoxS, we compared MarA, MarA mutants, and SoxS for their abilities to activate 16 promoters and to bind their cognate marbox binding sites. Replacement of the MarA glutamic acid residue 89 with alanine greatly increased the marbox binding and activation of many class I promoters. Like cells constitutive for SoxS, cells expressing the MarA with the E89A mutation were more resistant to superoxides than those harboring WT MarA. The activities of several other E89 substitutions ranked as follows: E89A > E89G > E89V > WT > E89D. Increased binding and activation occurred only at class I promoters when the 12th base of the promoter's marbox (a position at which there is no known interaction between the marbox and MarA) was not a T residue. Furthermore, WT MarA binding to a synthetic marbox in vitro was enhanced when the phosphate group between positions 12 and 13 was eliminated on one strand. The results demonstrate that relatively minor changes in a single amino acid side chain (e.g., alanine to valine or glutamic acid to aspartic acid) can strongly influence activity despite any evidence that the side chain is involved in positive interactions with either DNA or RNA polymerase. We present a model which attributes the differences in binding and activation to the interference between the Beta- and gamma-carbons of the amino acid at position 89 and the phosphate group between positions 12 and 13.
Ann file
T1 Species 128 144 Escherichia coli
N1 Reference T1 Taxonomy:562
T2 Species 227 243 Escherichia coli
N2 Reference T2 Taxonomy:562