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In bacteria, an enzyme called dam methylase (Deoxyadenosine methylase) methylates adenines (A) in the sequence GATC in the new strand formed after replication. What role does this methylation play? I read that it has something to do with proofreading. If this is so, then how?

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The dam methylase has three different functions:

  1. Correction replication errors, since the new DNA molecule is only hemimethylated (the old strand is methylated, the newly synthesized is not). Since the proof-reading only takes place on the new strand, errors introduced during replication can be corrected.
  2. Regulation of replication: The ori of the chromosome is methylated to ensure that is only replicated once.
  3. Regulation of transcription: Methylation of GATC sequences promote the transcription of genes.

For further details see the references.

References:

  1. The great GATC: DNA methylation in E. coli
  2. The dam and dcm strains of Escherichia coli--a review.
  3. Dam methylation: coordinating cellular processes.
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