In the cell cycle (G1-S-G2-M), all of the DNA is replicated during the S or Synthesis stage. The cell may then spend some considerable time in the G2 phase before splitting in the M phase. Since there is double the amount of genetic material in the G2 phase, what mechanism if any, prevents the amount of gene expression from also doubling?
When the double strand is duplicated, the old strand (or, in other terms, the template) is methylated : this modification is enough to prevent the bind by the RNApol system and, by so, the transcription. By methylation, DNA-repair systems are able to detect which is the newer strand, to discover and fix replication errors.
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