Direct reversal of damage Although it might seem that direct reversal of damage would be the simplest way to correct the damage, in most cases the reverse reaction is not possible for thermodynamic or kinetic reasons. In a few cases, the reaction is reversible, and in some of these cases mechanisms have been developed to take advantage of that reversibility. The best studied of these is photoreversal of CPDs by the enzyme, CPD photolyase. CPD photolyase contains two chromophores responsible for absorbing light energy. This enzyme appears to be present in all living organisms.
Additional repair requires the synthesis of new enzyme molecules.
A final example of direct damage reversal is the sealing of a subset of nicks in DNA by DNA ligase. Nicks with other configurations, or nicks accompanied by additional backbone or base damage, require more complicated excision repair mechanisms. This page was last updated on September 17, 2000.