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Conversation 11: No. 1

category image Volume: Conversation 11
Issue Number 1
May 2000
ISBN 0-940030-80-2

Structure and Dynamics of the Tetrameric Mnt Repressor and a Model for its DNA Complex

The tetrameric Mnt repressor of bacteriophage P22 consists of two dimeric DNA-binding domains and a tetramerization domain. The NOE and chemical shift data demonstrate that the structures of the domains in the wild-type repressor protein are similar to those of the separate domains, the three-dimensional structures of which have been determined previously. 15N relaxation measurements show that the linker that connects the anti-parallel four-helix bundle with the two b-sheet DNA-binding dimers is highly flexible. No evidence was found for interactions between the distinct modules. The 15N relaxation properties of the two domains differ substantially, confirming their structural independence. A model in which one two-stranded coiled coil of the four-helix bundle is attached to one N-terminal dimer is most consistent with the biochemical data and15N relaxation data. For the Mnt-DNA complex this geometry fits with a model in which the two b-sheet DNA-binding domains are bound at two successive major grooves of the Mnt operator and the tetramerization domain is packed between these two DNA-bound dimers. In such a model the two-fold symmetry axis of the four-helix bundle coincides with that of the operator sequence and the two bound dimers. Bending of the Mnt operator of approximately 30° upon binding of the tetramer, as measured by gel-shift assays, is in agreement with this model of the Mnt-DNA complex.

Irene M.A. Nooren
Gert E. Folkers
Robert Kaptein
Robert T. Sauera
and Rolf Boelens

Department of NMR Spectroscopy
Bijvoet Center for Biomolecular Research
Utrecht University
Padualaan 8
3584 CH, Utrecht, The Netherlands
aDepartment of Biology
Massachusetts Institute of Technology
Cambridge, Massachusetts 02139

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