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Characterization of the DNA Binding Domain of StbA, A Key Protein of A New Type of DNA Segregation SystemCharacterization of the DNA Binding Domain of StbA, A Key Protein of A New Type of DNA Segregation SystemQuèbre V, Del Campo I, Cuevas A, Siguier P, Rech J, Le PTN, Ton-Hoang B, Cornet F, Bouet JY, Moncalian G, de la Cruz F, Guynet C.2022-10-14T22:00:00Z<h3>Abstract<br></h3><div> <br> </div><div>Low-copy-number plasmids require sophisticated genetic devices to achieve efficient segregation of plasmid copies during cell division. Plasmid R388 uses a unique segregation mechanism, based on StbA, a small multifunctional protein. StbA is the key protein in a segregation system not involving a plasmid-encoded NTPase partner, it regulates the expression of several plasmid operons, and it is the main regulator of plasmid conjugation. The mechanisms by which StbA, together with the centromere-like sequence stbS, achieves segregation, is largely uncharacterized. To better understand the molecular basis of R388 segregation, we determined the crystal structure of the conserved N-terminal domain of StbA to 1.9 Å resolution. It folds into an HTH DNA-binding domain, structurally related to that of the PadR subfamily II of transcriptional regulators. StbA is organized in two domains. Its N-terminal domain carries the specific stbS DNA binding activity. A truncated version of StbA, deleted of its C-terminal domain, displays only partial activities in vivo, indicating that the non-conserved C-terminal domain is required for efficient segregation and subcellular plasmid positioning. The structure of StbA DNA-binding domain also provides some insight into how StbA monomers cooperate to repress transcription by binding to the stbDR and to form the segregation complex with stbS.</div> <br><p><a href="">​J Mol Biol. 2022 Oct 15;434(19):167752.</a><br></p>421