Nucleotide Excision Repair in E. Coli a

Nucleotide excision repair (NER) is a generalized repair system capable of removing a large number of DNA lesions that differ widely in their chemical structure and conformation. NER is a highly conserved process and can be described in four basic steps. Genetic insult results in conformational change in the DNA helix, which serves as a binding site for damage recognition proteins. The binding of these proteins at a damaged site serves as a scaffold for the formation of an endonuclease complex that hydrolyzes the phosphodiester bond in two places near the damaged site. In E. coli, the incision sites are 7 nucleotides 5{prime} and 3 or 4 nucleotides 3{prime} to the damaged site, whereas it has been reported that in mammalian cells incisions occur approximately 27-29 nucleotides 5{prime} and 5 nucleotides 3{prime} to the damaged site. Following incision, the damaged site and the flanking nucleotides are removed, and DNA polymerase fills the excised gap. The process is completed by the ligation of the newly complete repair patch into the parental DNA. Nucleotide excision repair is a complex process, performed by a multiprotein machine. This complexity is underscored by the number of genetic loci, which, if mutated, can lead to inefficientmore » damage recognition and incision. During the last decade, using modern molecular techniques, several laboratories have cloned and characterized nucleotide excision repair genes from several organisms. Simultaneously, cell-free assays have been developed that can be used to characterize the specific protein products encoded by these genes. Due to its relative simplicity and ease of manipulation, the bacteria Escherichia coli has served as a model system for elucidation of the molecular details of nucleotide excision repair in other organisms. This paper briefly highlights some of the important features of nucleotide excision repair in E. coli.« less