Introduction to Genetic Analysis 471

Introduction to Genetic Analysis 471 - 470 Chapter 14...

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Unformatted text preview: 470 Chapter 14 Mutation, Repair, and Recombination Nucleotide excision repair Base excision repair can cor- rect only damaged bases that can be removed by a specific DNA glycosylase. However, there are more ways to dam- age a base than there are glycosylases to remove them. Thus, another system is required to repair the damage that the glycosylases cannot. Rather than recognize a particular damaged base, the nucleotide excision-repair system de- tects distortions in the double helix caused by the pres- ence of an abnormal base (see Figure 14-25c). Mutations that cause such distortions include the pyrimidine dimers caused by UV light and the addition of aflatoxin to gua- nine residues. Detection of a distortion initiates a multistep repair process involving many proteins. In E. coli , a com- plex consisting of three enzymatic activities encoded by the uvrABC genes detects the distortion and cuts the dam- aged strand at two sites flanking the lesion (Figure 14-28)....
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