5.2 DNA Repair Mechanisms

What is the damage addressed in Mismatch Repair (MMR)?

Mismatches due to DNA replication errors, such as incorporating a non-complementary base

When is Mismatch Repair (MMR) used?

After DNA replication, before the cell enters mitosis.

What are the Key Players in Mismatch Repair (MMR)?

Proteins like MutS, MutL and MutH in bacteria and MSH and MLH in humans.

What is the damage addressed in Base Excision Repair (BER)?

Small, non-helix-distorting base lesions caused by deamination, oxidation, or alkylation damage

When is Base Excision Repair (BER) used?

Anytime during the cell cycle.

What are the Key Players in Base Excision Repair (BER)?

DNA glycosylases, AP endonuclease (APE1), DNA polymerase, and DNA ligase.

What is the damage addressed in Nucleotide Excision Repair (NER)?

Bulky, helix-distorting lesions, such as those caused by UV light-induced pyrimidine dimers.

When is the Nucleotide Excision Repair (NER) used?

Anytime during the cell cycle

What are the Key Players in Nucleotide Excision Repair (NER)?

Multiple, including XPC, XPA-XPG and the TFIIH complex.

What is the damage addressed in Homologous Directed Repair (HDR)?

Double-strand breaks (DSBs), especially those occurring during the S or G2 phases of the cell cycle when a sister chromatid is available as a template.

When is the Homologous Directed Repair used?

Preferentially during the S and G2 phases.

What are the Key Players in Homologous Directed Repair (HDR)?

BRCA1, BRCA2, RAD51, and several other proteins.

What is the damage addressed in Non-Homologous End Joining (NHEJ)?

Double-strand breaks (DSBs). This pathway is more error-prone than HDR as it directly ligates the broken ends without a need for a homologous template.

When is the Non-Homologous End Joining (NHEJ) used?

Anytime during the cell cycle, but especially during G1.

What are the Key Players in Non Homologous End Joining (NHEJ)?

Ku70/80 heterodimer, DNA-PKcs.

What is the damage addressed in Direct Damage Reversal?

Specific cases of direct damage reversal include repair of O6-methylguanine by O6-methylguanine DNA methyltransferase (MGMT) and photoreactivation of UV-induced pyrimidine dimers by photolyase (in organisms that possess this enzyme, not in humans).

When is Direct Damage Reversal used?

Anytime during Cell cycle

What is the damage addressed in Translesion Synthesis (TLS)?

Bulky DNA lesions that stall replication forks.

When is Translesion Synthesis (TLS) used?

Primarily during DNA replication

What are the Key Players in Translesion Synthesis (TLS) used?

Specialized DNA polymerases (e.g., Pol V in bacteria and Pol η, Pol ι, Pol κ in eukaryotes).