1.15.16 DNA Repair Fidelity Definition

DNA Repair Fidelity Definition is a description of the degree to which a given DNA repair process restores the original, pre-damage DNA sequence at the site of a lesion, expressed as the likelihood that the repaired DNA precisely matches the sequence present before the damage occurred, as opposed to containing small insertions, deletions, substitutions, or other alterations introduced during the repair process itself.

Conceptual Basis

Fidelity as a Property of the Repair Outcome

DNA repair fidelity concerns the accuracy of the outcome produced by a repair process, distinct from whether repair occurs at all; a lesion can be repaired rapidly and completely in the sense that the physical damage is resolved, while the resulting sequence nonetheless differs from the original, reflecting low fidelity in the specific outcome of that repair event.

A Spectrum Rather Than a Binary Property

DNA repair fidelity is best understood as a spectrum ranging from processes that reliably restore the exact original sequence to processes that reliably introduce some degree of sequence alteration as an inherent feature of their mechanism, rather than as a strict binary distinction between accurate and inaccurate repair.

Determinants of Repair Fidelity

Availability and Use of a Template

A principal determinant of repair fidelity is whether the repair process relies on an accurate, sequence-identical template to guide resynthesis of the damaged region; pathways that use such a template are generally capable of higher fidelity than pathways that resolve damage without reference to a template sequence.

Mechanism of End or Gap Processing

For lesions requiring physical processing of DNA ends or gaps prior to resynthesis, the specific processing steps involved, including any trimming or modification of the DNA termini, contribute to repair fidelity by determining how closely the processed ends or gap correspond to the original, undamaged sequence configuration.

Pathway Selection for a Given Lesion

Because different repair pathways offer differing degrees of fidelity, the specific pathway selected to resolve a given lesion, among those capable of acting on that lesion type, is itself a determinant of the overall fidelity with which that lesion is ultimately resolved.

Fidelity Across Repair Pathways

Comparatively High-Fidelity Repair

Repair processes that rely on an intact, homologous template, such as homologous recombination repair for double-strand breaks and mismatch repair for replication errors, are characterized by comparatively high fidelity, since the template provides a reliable reference for restoring the correct original sequence.

Comparatively Lower-Fidelity Repair

Repair processes that resolve damage without reference to a homologous template, such as nonhomologous end joining for double-strand breaks, are characterized by comparatively lower fidelity, since the absence of a template means that the processing steps required to rejoin or bypass the damage are more likely to introduce small sequence alterations.

Significance for Genome Integrity

Fidelity as a Determinant of Mutation Accumulation

Because the fidelity of repair directly determines whether a resolved lesion leaves the original sequence intact or introduces a new alteration, the overall fidelity of the repair processes operating within a cell is a principal factor governing the rate at which mutations accumulate as a consequence of DNA damage and its resolution.

Shifts in Fidelity as a Contributor to Genome Instability

A shift within a cell toward greater reliance on comparatively lower-fidelity repair pathways, whether due to loss of a higher-fidelity alternative or to conditions favoring the lower-fidelity route, directly elevates the rate at which repair-associated sequence alterations accumulate, linking changes in the balance of repair fidelity to the broader phenomenon of genome instability.