Question

How does the nucleotide excision repair (NER) system in E. coli work, and what kinds of DNA damage does it repair?

Answer 1

Ans-

Nucleotide excision repair will act on the damaged areas of Deoxyribonucleic acid(DNA). In nucleotide excision repair system will cleave the phosphodiester bond on both side of lesion it is generally a thymine dimer which is formed after DNA is exposed to UV radiation. The bond is cleaved on the strand having the thymine dimer which results in excision of short segment of nucleotide called oligonucleotide.
After excision, there is a gap which is filled by the enzyme DNA polymerase and ligated by enzyme Ligase.
For example- Uvr system in E.coli in this oligonucleotide is excised
Enzyme is ABC exinuclease at the site of lesion it will bind to double-stranded DNA. Lesion like thymine dimer.
In this Uvr A and Uvr B will attach to the double stranded DNA at the lesion site. A site where thymine dimer is formed when DNA is exposed to UV radiation.
After this Uvr A will leave and it will allow the Uvr C to come and bind thus forming the dimer of Uvr BC
Now, Uvr BC will cleave the phosphodiester bond at the lesion site and as a result of which a short oligonucleotide sequence is removed.
Uvr D generally the helicase enzyme will unwind the strand of DNA and single strand is released between cuts.
DNA polymerse will now synthesize the nucleotide bases and ligase will join the phosphodiester bond between the bases formed by DNA polymerase.

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