Mismatch repair system - (Fig 5.25 Eukaryotes have a...

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Mismatch repair system . Recognizes mismatches resulting from replication. Scans newly replicated DNA, identifies mismatch, excises the mismatched base specifically from new strand so error can be repaired. How can the old strand of DNA be distinguished from the new strand after replication? In E. coli , because new strand not yet methylated at GATC sequences as is normally the case (A of GATC methylated). In E. coli mismatch repair is initiated by the protein MutS , which recognizes mismatch, and forms complex with MutL and MutH . Then MutH (an endonuclease) cleaves the unmethylated DNA strand at a GATC sequence
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Unformatted text preview: (Fig. 5.25). Eukaryotes have a similar mismatch repair system, but the mechanism by which they identify the newly replicated DNA strand is not known. If DNA contains damaged bases (like a pyrimidine dimer) that cannot be repaired, replication and transcription are blocked at this site. However, there are mechanisms to circumvent the damaged site. For example, replication can be initiated downstream of the damaged site by an Okazaki fragment. The result is a gap in the new daughter strand opposite the damage of the parental strand....
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