Cooperative binding of DctD to the dctA upstream activation sequence of Rhizobium meliloti is enhanced in a constitutively active truncated mutant

Dean Scholl, B. Tracy Nixon

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DctD, a σ54-dependent, two-component regulator, binds to promoter distal (A) and promoter proximal (B) sites in an activation sequence located upstream of the dctA promoter. We report gel filtration and quantitative DNase I footprint experiments supporting a model in which DctD2 binds to these sites cooperatively. The global analysis of upstream activation sequences containing sites A and B, A and B one-half helical turn out of phase, and only B yielded values for the intrinsic and cooperative binding free energies of ΔG(A)0 = -9.5 ± 0.3, ΔG(B)0 = -11.2 ± 0.2, and ΔG(AB)0 = -2.5 ± 0.5. A separate analysis of data from upstream activation sequences containing site A and a point mutant of site B, and site A and mutant site B one-half helical turn out of phase confirmed the estimate of cooperativity, yielding free energy values of ΔG(A)0 = -9.4 ± 0.2, ΔG(B((G→C) = -10.0 ± 0.2, and ΔG(AB(G→C) = -2.2 ± 0.4. We previously showed that removing the two-component receiver domain from DctD, making DctD(Δ)(1-142), yields a constitutively active truncated protein. Global analysis of binding data for DctD(Δ)(1-142) showed that this constitutively active mutant has intrinsic binding energies equal to that of the inactive DctD protein, but that it displays significantly higher cooperativity (ΔG(A)0 = -9.4 ± 0.6, ΔG(B)0 = -11.1 ± 0.3, and ΔG(AB)0 = -3.8 ± 0.6.).

Original languageEnglish (US)
Pages (from-to)26435-26442
Number of pages8
JournalJournal of Biological Chemistry
Issue number42
Publication statusPublished - Oct 29 1996


All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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