NORMAL GENOMIC

• Kwon HJ, Bennik MH, Demple B, Ellenberger T
• Crystal structure of the Escherichia coli Rob transcription factor incomplex with DNA.
• Nat Struct Biol. 2000; 7: 424-30
• Display abstract

• The Escherichia coli Rob protein is a transcription factor belonging tothe AraC/XylS protein family that regulates genes involved in resistanceto antibiotics, organic solvents and heavy metals. The genes encodingthese proteins are activated by the homologous proteins MarA and SoxS,although the level of activation can vary for the different transcriptionfactors. Here we report a 2.7 A crystal structure of Rob in complex withthe micF promoter that reveals an unusual mode of binding to DNA. TheRob-DNA complex differs from the previously reported structure of MarAbound to the mar promoter, in that only one of Rob's dual helix-turn-helix(HTH) motifs engages the major groove of the binding site. Biochemicalstudies show that sequence specific interactions involving only one ofRob's HTH motifs are sufficient for high affinity binding to DNA. The twodifferent modes of DNA binding seen in crystal structures of Rob and MarAalso match the distinctive patterns of DNA protection by AraC at severalsites within the pBAD promoter. These and other findings suggest that geneactivation by AraC/XylS transcription factors might involve twoalternative modes of binding to DNA in different promoter contexts.