Excision Repair by the Uvr System

General Description

Excision repair by the Uvr System is a DNA repair mechanism that removes a wide variety of damaged nucleotides and determines the correct sequence from the complementary DNA strand using (A)BC exinuclease. This complex is made up of a few proteins, UvrA, UvrB, and UvrC, which carry out coordinated actions to complete the excision repair. Uvr proteins are necessary to repair damage caused by ultraviolet light in genomes. Mutants of the uvrgenes are very sensitive to killing by UV irradiation and are incapable of removing thymine-thymine and thymine-cytosine adducts.

UvrA is the first of four proteins that largely assists in excision repair and is responsible for first scanning DNA for distortions. Once a genome distortion, such as those caused by a thymine dimer or another chemical adduct on a base, is detected by UvrA, UvrA guides UvrB to the lesion in the DNA. The DNA is bent by approximately 130° and UvrB proceeds to melt the DNA, unwinding the area around the lesion by about 5bp to a bubble. It is necessary that UvrA dissociates from the UvrB-DNA complex before UvrC can bind to the complex. Once it does, the 3’ incision is made by UvrB while the 5’ incision is made by UvrC. This cleavage excises the area of the bubble, including the lesion, creating a short, single-stranded DNA segment that is then removed by DNA helicase, UvrD. DNA polymerase uses the undamaged, complementary strand as a template to fill the gap that results from the excision, and DNA ligase forms covalent phosphodiester bonds between the 3’ hydroxyl ends of one nucleotide with the 5’phosphate end of another. Once complete, the original nucleotide sequence is restored.

Notes

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Related GO Terms

Help:Gene Ontology

References

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