CytR/cAMP-CRP Nucleoprotein Formation inE. coli: The CytR Repressor Binds its Operator as a Stable Dimer in a Ternary Complex with cAMP-CRP

Flexibility and Adaptability in Binding of E. coli Cytidine Repressor to Different Operators Suggests a Role in Differential Gene Regulation

“…Several assumptions implicit in this model have each been evaluated separately and discussed previously. These are: first, the quantum yield of OG does not change when CytR binds to these olgionucleotides; 20 second, dimer is the oligomeric species of CytR that binds individual operator palindromes, 6,12,17,21 third, free CytR remains homogeneous dimer over the concentration range and conditions of the experiments; 12 and fourth, binding is thermodynamically reversible. 18 …”

Design of CytR regulated, cAMP-CRP dependent class II promoters in Escherichia coli: RNA polymerase-promoter interactions modulate the efficiency of CytR repression

“…cAMP-CRP dependent activation of deoP2 primarily depends on the downstream CRP-1 site (Sùgaard-Andersen et al, 1991a). CytR repression of deoP2 involves binding of a CytR dimer in concert with cAMP-CRP and results in the formation of a nucleoprotein complex in which the CytR dimer is sandwiched between the two cAMP-CRP complexes at CRP-1 and CRP-2 (Kristensen et al, 1996;Pedersen et al, 1991). This binding is cooperative and depends on direct protein-protein contacts between CytR and cAMP-CRP (Pedersen et al, 1991;Sùgaard-Andersen et al, 1991b;Sùgaard-Andersen & Valentin-Hansen, 1993).…”

“…b The dissociation constant, K d , was determined as the protein concentration at which half of the labelled DNA fragments were retarded as described for (Kristensen et al, 1996). CytR or cAMP-CRP were equilibrated with 32 P-labelled promoter fragment and subjected to EMSA as described in Experimental Procedures.…”

Allosteric Mechanism of Induction of CytR-regulated Gene Expression

“…2 More recent analysis of gel mobility shift assays of CytR binding to DNA has been interpreted to indicate that CytR remains as stable dimer over the range of concentrations at which it binds DNA operators (11). Based on these data, the binding experiments were analyzed according to the simplest model in which CytR exists only as dimer.…”