Figure 4.

The interactions between SspA, the σ⁷⁰R4 and the ZBD of RNAP-β′ subunit: binding affinity data. (A) Binding affinities between wild-type SspA or SspA-H85A and σ⁷⁰-RNAP measured by a fluorescence polarization (FP) assay. varying amounts of the σ⁷⁰-RNAP as indicated (mean ± SEM; three determinations). (B) Relative binding affinities of wild-type SspA and its mutants from the σ⁷⁰R4-SspA interface or ZBD of β′ subunit-SspA interface measured by the fluorescence polarization assay (mean ± SEM; three determinations). Error bars represent mean± SEM out of n = 3 experiments. (C) Protein Sequence Alignments of SspA from ∼100 non-redundant bacterial species. The sequences were extracted from UniProt Database by BLAST. The alignment was performed by Cluster Omega and the sequence logos were generated on the WebLogo server (http://weblogo.berkeley.edu/logo.cgi). Black filled circles, residues involved in interactions with the ZBD from RNAP-β′ subunit; Red filled circles indicate residues that are involved with interactions with σ⁷⁰R4. The residues are numbered as in E. coli SspA.