Very-short-patch repair (Vsr) enzymes occur in a variety of bacteria, where they
initiate nucleotide excision repair of G:T mismatches arising by deamination of
5-methyl-cytosines in specific regulatory sequences. We have now determined the
structure of the archetypal dcm-Vsr endonuclease from Escherichia coli bound to
the cleaved authentic hemi-deaminated/hemi-methylated dcm sequence 5'-C-OH-3'
5'-p-T-p-A-p-G-p-G-3'/3'-G-p-G-p-T-p(Me5)C-p-C formed by self-assembly of a
12mer oligonucleotide into a continuous nicked DNA superhelix. The structure
reveals the presence of a Hoogsteen base pair within the deaminated recognition
sequence and the substantial distortions of the DNA that accompany Vsr binding
to product sites.
