Nucleic Acids Research Advance Access originally published online on April 10, 2007
Nucleic Acids Research 2007 35(8):2643-2650; doi:10.1093/nar/gkm129
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Nucleic Acids Research, 2007, Vol. 35, No. 8 2643-2650
© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Molecular Biology |
DNA structural deformations in the interaction of the controller protein C.AhdI with its operator sequence
Biophysics Laboratories, Institute of Biomedical and Biomolecular Science, St Michael's Building, University of Portsmouth, PO1 2DT, UK
*To whom correspondence should be addressed. Tel: 02392 842 678; Fax: 02393 842 053; Email: kneale{at}port.ac.uk
Received January 22, 2007. Revised February 15, 2007. Accepted February 18, 2007.
Controller proteins such as C.AhdI regulate the expression of bacterial restrictionmodification genes, and ensure that methylation of the host DNA precedes restriction by delaying transcription of the endonuclease. The operator DNA sequence to which C.AhdI binds consists of two adjacent binding sites, OL and OR. Binding of C.AhdI to OL and to OL + OR has been investigated by circular permutation DNA-bending assays and by circular dichroism (CD) spectroscopy. CD indicates considerable distortion to the DNA when bound by C.AhdI. Binding to one or two sites to form dimeric and tetrameric complexes increases the CD signal at 278 nm by 40 and 80% respectively, showing identical local distortion at both sites. In contrast, DNA-bending assays gave similar bend angles for both dimeric and tetrameric complexes (47 and 38°, respectively). The relative orientation of C.AhdI dimers in the tetrameric complex and the structural role of the conserved Py-A-T sequences found at the centre of C-protein-binding sites are discussed.
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