Clue to damage recognition by UvrB: residues in the beta-hairpin structure prevent binding to non-damaged DNA.
UvrB, the ultimate damage-recognizing component of bacterial nucleotide excision repair, contains a flexible beta-hairpin rich in hydrophobic residues. We describe the properties of UvrB mutants in which these residues have been mutated. The results show that Y101 and F108 in the tip of the hairpin are important for the strand-separating activity of UvrB, supporting the model that the beta-hairpin inserts between the two DNA strands during the search for DNA damage. Residues Y95 and Y96 at the base of the hairpin have a direct role in damage recognition and are positioned close to the damage in the UvrB-DNA complex. Strikingly, substituting Y92 and Y93 results in a protein that is lethal to the cell. The mutant protein forms pre- incision complexes on non-damaged DNA, indicating that Y92 and Y93 function in damage recognition by preventing UvrB binding to non-damaged sites. We propose a model for damage recognition by UvrB in which, stabilized by the four tyrosines at the base of the hairpin, the damaged nucleotide is flipped out of the DNA helix.
Moolenaar
G F
GF
Laboratory of Molecular Genetics, Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, Einsteinweg 55, 2300 RA Leiden, The Netherlands.
Höglund
L
L
Goosen
N
N
D019943:Amino Acid Substitution; D001407:Bacillus / Q000235:genetics; D001665:Binding Sites / Q000502:physiology; D004249:DNA Damage / Q000502:physiology*; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair / Q000502:physiology*; D004269:DNA, Bacterial / Q000378:metabolism* / Q000528:radiation effects; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000378:metabolism / Q000528:radiation effects; D017433:Protein Structure, Secondary / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D014466:Ultraviolet Rays
D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; C058093:UvrB protein, E coli; D004265:DNA Helicases