Cover: The controller protein of the bacterial restriction-modification system Esp1396 acts as both a transcriptional activator and repressor. The crystal structure of the nucleoprotein complex reveals significant bending of the operator DNA and a dramatic widening of the major groove (centre of figure). The strong ion-pair interactions between amino acid residues at the dimer-dimer interface, together with an expansion of the DNA major groove, suggest a mechanism for cooperative binding of adjacent dimers that governs the switch from activation to repression. For further details, see the article by McGeehan et al. (Nucleic Acids Res., 2008; 36: 4778–4787).
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