Nucleic Acids Research, 1984, Vol. 12, No. 8 3551-3561
© 1984
CHEMISTRY |
1H NMR sudy of the interaction of bacteriophage
Cro protein with the OR3 operator. Evidence for a change of the conformation of the OR3 operator on binding
+Institute of Biophysical Chemistry, University of Frankfurt D-6000 Frankfurt/Main 70, FRG *Institute of Molecular Biology, USSR Academy of Sciences Vavilov Street 32, Moscow B-334, USSR
Received March 12, 1984. Accepted April 5, 1984.
The specific complex between the 
phage OR3 operator and the Cro protein has been studied by proton NMR spectroscopy atR500 MHz. The DNA imino proton resonances of this complex have been assigned to specific base pairs using the known assignments of these resonances for the free operator. Increase of the protein/DNA ratio to complete saturation of the OR3 operator with the Cro protein made it possible to follow the shifts changes of the resonances. Ambiguities were resolved by nuclear Overhauser effect measurements on the complex. The shifts of the imino proton resonance positions provide information on the changes induced in the conformation of the operator upon complex for mation with a dimer of the Cro protein. The most striking shift occurs for the central (GC 9) base pair, which is known to have no direct contacts with the Cro protein. This shift may be induced by a bend in the OR3 operator DNA at the GC 9 base pair to accomodate the operator for the binding of the Cro protein dimer. The imino proton resonances of two additional base pairs can be observed in the complex, demonstrating an overall stabilization of the DNA structure by the binding of the Cro protein.