It is complementary to a highly conserved sequence close to the 3’ end of 16S rRNA.

The rRNA sequence is the hexamer:

3’. . . U C C U C C . . . 5’

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In Escherichia coli MMR system, MutL, in turn, activates MutH, an enzyme that causes an incision or nick on one strand near the site of the mismatch.

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Nicking is followed by the action of a specific helicase (UvrD) and one of three exonucleases.

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Eukaryotic cells also repair mismatches and do so using homologs to MutS (called MSH proteins for “MutS homologs”) and MutL (called MLH and PMS

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In BER, A DNA glycosylase recognizes a damaged base (in this case, a uracil) and cleaves between the base and deoxyribose in the backbone.

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n BER,  An AP endonuclease cleaves the phosphodiester backbone near the AP site

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#Unit 3. Fundamental Processes

In BER,  DNA polymerase I initiates repair synthesis from the free 3’ hydroxyl at the nick, removing (with its 5’-3’ exonuclease activity) and replacing a portion of the damaged strand.