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The phage 434 OR2/R1-69 complex at 2.5 A resolution
1Howard Hughes Medical Institute, Harvard University Department of Biochemistry and Molecular Biology, Cambridge, MA 02138.
Journal of Molecular Biology
|August 5, 1993
Summary
The bacteriophage 434 repressor binds DNA, maintaining its backbone structure but altering base-pair conformations. This DNA-protein interaction influences repressor affinity for different operator sites.
Area of Science:
- Structural biology
- Molecular biology
- Biochemistry
Background:
- Bacteriophage 434 repressor regulates viral gene expression by binding to operator DNA sequences.
- Understanding repressor-operator interactions is crucial for deciphering gene regulation mechanisms.
Purpose of the Study:
- To determine the crystal structure of the bacteriophage 434 repressor (R1-69) bound to the OR2 operator DNA sequence.
- To compare the structural details of the R1-69/OR2 complex with the previously determined R1-69/OR1 complex.
Main Methods:
- X-ray crystallography was used to determine the crystal structure.
- The structure was resolved to 2.5 A resolution.
- Comparative analysis of the OR1 and OR2 complex structures.
Main Results:
- The DNA-binding domain of bacteriophage 434 repressor (R1-69) was crystallized with a 20 base-pair OR2 operator DNA fragment.
- The overall DNA backbone conformation and protein-DNA interaction patterns were conserved between the OR1 and OR2 complexes.
- Significant differences were observed in the base-pair conformations, with OR2 exhibiting more co-planar central base-pairs and lacking cross-strand bifurcated hydrogen bonds.
Conclusions:
- Protein binding induces a specific, well-defined backbone conformation in operator DNA.
- Sequence-dependent energetic costs of achieving this conformation likely influence repressor-operator binding affinity.
- Structural insights provide a basis for understanding differential binding affinities of repressors to various operator sequences.