DNA damage limitation

The damage caused to the sequence and structure of a DNA helix must be repaired through the cellular machinery before efficient replication and transcription can start again. If the damage is not repaired then the mutation will become inherited through subsequent generations. The existence of modified bases signals the induction of systems designed to remove specific types of damage. Some types of damage can be corrected through an enzyme-catalyzed reversal of the nucleotide modification but more lasting damage means that stretches of one strand of DNA must be removed and replaced with new nucleotides. There are limitations to the capacity of the cell to repair its own DNA in that in most cases the repair machinery relies on a correct template against which to make corrections. If both sides of the helix example for both base pairs are damaged then the cell is less likely to correct the error. Thus events that cause deletion of regions of the DNA are more likely to be inherited than those that only damage one strand, or a few bases of one strand of the helix.

Although DNA repair systems are extremely efficient in organisms like as the Bacterium Deinococcus radiodurans and the Archaeon Pyrodictium abyssi there is a greater error in DNA repair mechanisms than in DNA replication. The systems described here are specific for the Bacteria but analogous ones exist in the Archaea and the eukaryotes.