The E. coli NusA carboxy-terminal domains are structurally similar and show specific RNAP- and λN interaction

摘要

The carboxy-terminal domain of the transcription factor Escherichia coli NusA, NusACTD, interacts with the protein N of bacteriophage λ, λN, and the carboxyl terminus of the E. coli RNA polymerase α subunit, αCTD. We solved the solution structure of the unbound NusACTD with high-resolution nuclear magnetic resonance (NMR). Additionally, we investigated the binding sites of λN and αCTD on NusACTD using NMR titrations. The solution structure of NusACTD shows two structurally similar subdomains, NusA(353–416) and NusA(431–490), matching approximately two homologous acidic sequence repeats. Further characterization of NusACTD with 15N NMR relaxation data suggests that the interdomain region is only weakly structured and that the subdomains are not interacting. Both subdomains adopt an (HhH)2 fold. These folds are normally involved in DNA–protein and protein–protein interactions. NMR titration experiments show clear differences of the interactions of these two domains with αCTD and λN, in spite of their structural similarity.