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Updated: Mar 8, 2026
Proofreading and DNA Repair Assay Using Single Nucleotide Extension and MALDI-TOF Mass Spectrometry Analysis
Published on: June 19, 2018
A non-canonical mismatch repair pathway in prokaryotes
A Castañeda-García1,2, A I Prieto1, J Rodríguez-Beltrán1
1Stress and Bacterial Evolution Group, Instituto de Biomedicina de Sevilla. Avda. Manuel Siurot S/N, 41013-Sevilla, Spain.
Abstract:
Mismatch repair (MMR) is a near ubiquitous pathway, essential for the maintenance of genome stability. Members of the MutS and MutL protein families perform key steps in mismatch correction. Despite the major importance of this repair pathway, MutS-MutL are absent in almost all Actinobacteria and many Archaea. However, these organisms exhibit rates and spectra of spontaneous mutations similar to MMR-bearing species, suggesting the existence of an alternative to the canonical MutS-MutL-based MMR. Here we report that Mycobacterium smegmatis NucS/EndoMS, a putative endonuclease with no structural homology to known MMR factors, is required for mutation avoidance and anti-recombination, hallmarks of the canonical MMR. Furthermore, phenotypic analysis of naturally occurring polymorphic NucS in a M. smegmatis surrogate model, suggests the existence of M. tuberculosis mutator strains. The phylogenetic analysis of NucS indicates a complex evolutionary process leading to a disperse distribution pattern in prokaryotes. Together, these findings indicate that distinct pathways for MMR have evolved at least twice in nature.
Insights
Genome stability is maintained by mismatch repair (MMR). This study reveals Mycobacterium smegmatis NucS/EndoMS as a novel MMR factor, distinct from the canonical MutS-MutL pathway, indicating alternative MMR evolution.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- Mismatch repair (MMR) is crucial for genome stability, typically involving MutS and MutL proteins.
- Many bacteria and archaea lack canonical MutS-MutL MMR but maintain similar mutation rates, suggesting alternative repair mechanisms.
Purpose of the Study:
- To identify alternative MMR pathways in organisms lacking canonical MutS-MutL.
- To investigate the role of Mycobacterium smegmatis NucS/EndoMS in mutation avoidance.
Main Methods:
- Functional analysis of Mycobacterium smegmatis NucS/EndoMS.
- Phenotypic analysis of NucS polymorphisms in a surrogate model.
- Phylogenetic analysis of NucS distribution.
Main Results:
- Mycobacterium smegmatis NucS/EndoMS, a novel endonuclease, is essential for mutation avoidance and anti-recombination.
- Naturally occurring NucS variants suggest potential mutator strains in Mycobacterium tuberculosis.
- Phylogenetic analysis reveals a complex evolutionary history and dispersed distribution of NucS.
Conclusions:
- Distinct MMR pathways have evolved independently at least twice in prokaryotes.
- NucS represents a novel, non-MutS/MutL MMR factor, highlighting evolutionary divergence in DNA repair.
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