Hinge-helix formation and DNA bending in various lac repressor-operator complexes.
The hinge-region of the lac repressor plays an important role in the models for induction and DNA looping in the lac operon. When lac repressor is bound to a tight-binding symmetric operator, this region forms an alpha-helix that induces bending of the operator. The presence of the hinge-helices is questioned by previous data that suggest that the repressor does not bend the wild-type operator. We show that in the wild-type complex the hinge-helices are formed and the DNA is bent, similar to the symmetric complex. Furthermore, our data show differences in the binding of the DNA binding domains to the half-sites of the wild-type operator and reveal the role of the central base-pair of the wild-type operator in the repressor-operator interaction. The differences in binding to the operator half-sites are incorporated into a model that explains the relative affinities of the repressor for various lac operator sequences that contain left and right half-sites with different spacer lengths.
Spronk
C A
CA
Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
Folkers
G E
GE
Noordman
A M
AM
Wechselberger
R
R
van den Brink
N
N
Boelens
R
R
Kaptein
R
R
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001483:Base Sequence; D003001:Cloning, Molecular; D029968:Escherichia coli Proteins; D007763:Lac Operon; D056968:Lac Repressors; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D011487:Protein Conformation; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism*
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D056968:Lac Repressors; D009838:Oligodeoxyribonucleotides; D012097:Repressor Proteins