Nucleotide excision repair

The removal of many nucleotides by UvrABC exinuclease and their replacement by DNA polymerase I and DNA ligase is ubiquitous in the Bacteria. In E. coli this mechanism has been shown to be largely error-free. It enables the removal of large areas of mutation example for as a result of the presence of pyrimidine dimers and is therefore known as nucleotide excision repair NER. The UvrABC system scans the genome and initiates the process in regions of distortion of the helix in Figure. Nucleotide excision repair differs from base excision repair in that the entire nucleotide is removed causing a complete break in one strand of the helix.

                                          Figure:  Methyl-directed mismatch repair.

                                    Figure:  Nucleotide excision  repair  of thymine  dimers.