DNA Repair Mechanisms in Escherichia coli

Escherichia coli relies on a sophisticated suite of pathways to maintain genomic integrity in the face of endogenous metabolic by-products and exogenous agents. Direct reversal mechanisms, exemplified by O6-methylguanine-DNA methyltransferase, remove simple alkyl adducts by transferring the lesion onto a dedicated active-site residue. Base-excison repair (BER) addresses a broad spectrum of non-bulky lesions: DNA glycosylases detect and excise damaged bases, generating abasic sites that are processed by AP endonucleases, exonucleases, polymerases and ligases to restore the correct nucleotide. Nucleotide-excision repair (NER) removes bulky, helix-distorting adducts through a coordinated incision–excision–resynthesis cycle driven by the UvrABC complex. Mismatch repair (MMR) corrects replication errors by recognising mispaired bases and directing excision of the nascent strand. Homologous recombination repair provides tolerance to double-strand breaks and stalled forks via RecA-mediated strand exchange. The inducible SOS response orchestrates global upregulation of damage-tolerance polymerases and repair factors under severe stress. Together, these pathways create a dynamic network that balances fidelity, flexibility and survival, underpinning E. coli’s adaptability in diverse environments and its utility as a model organism in biotechnology and medicine.

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Technical terms

Base-excision repair (BER): A pathway in which DNA glycosylases remove damaged bases, creating abasic sites that are processed and filled in by endonucleases, polymerases and ligases.

Abasic site: A location in DNA where the base has been removed, leaving the deoxyribose backbone intact but unpaired.

DNA glycosylase: An enzyme that recognises and excises specific damaged bases, initiating BER.

AP endonuclease: An enzyme that cleaves the phosphodiester backbone at abasic sites to allow repair synthesis.

Direct reversal: A repair mechanism that restores the original base by enzymatic removal of the adduct without cutting the DNA backbone.

3′-phosphoglycolate terminus: A blocking group at the 3′ end of a DNA strand break that must be removed before repair synthesis can proceed.

References

1. New substrates for old enzymes. 5-Hydroxy-2'-deoxycytidine and 5-hydroxy-2'-deoxyuridine are substrates for Escherichia coli endonuclease III and formamidopyrimidine DNA N-glycosylase, while 5-hydroxy-2'-deoxyuridine is a substrate for uracil DNA N-glycosylase.. Journal of Biological Chemistry (1994).
2. Homogeneous Escherichia coli endonuclease IV. Characterization of an enzyme that recognizes oxidative damage in DNA.. Journal of Biological Chemistry (1988).
3. Repair of alkylated DNA in Escherichia coli. Physical properties of O6-methylguanine-DNA methyltransferase.. Journal of Biological Chemistry (1982).