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Genetic recombination destabilizes (CTG)n.(CAG)n repeats in E. coli
Vera I Hashem1, William A Rosche, Richard R Sinden
1Laboratory of DNA Structure and Mutagenesis, Center for Genome Research, Institute of Biosciences and Technology, Texas A&M University, 2121 West Holcombe Blvd., Houston 77030-3303, USA.
Mutation Research
|September 29, 2004
Summary
Genetic instability in trinucleotide repeats, linked to neurological diseases, is reduced by mutations affecting recombination. Recombination proficiency correlates with higher trinucleotide repeat instability.
Area of Science:
- Genetics
- Molecular Biology
- Genomic Instability
Background:
- Trinucleotide repeat expansions are associated with 17 neurological diseases.
- Factors influencing trinucleotide repeat instability are of significant interest.
- Genes involved in DNA repair and replication impact repeat instability in model organisms.
Purpose of the Study:
- To investigate the role of specific DNA repair genes (recA, recB, lexA) in the instability of (CTG)n.(CAG)n trinucleotide repeats.
- To determine the effect of recombination proficiency on trinucleotide repeat deletion rates in Escherichia coli.
Main Methods:
- Utilized a genetic assay in E. coli to measure the rate of trinucleotide repeat deletion.
- Examined the impact of mutations in recA, recB, and lexA genes on repeat deletion rates.
- Assessed the influence of SOS system induction and the presence of triplet repeats on cellular responses.
Main Results:
- Mutations in recA and recB genes, which reduce recombination rates, significantly stabilized trinucleotide repeats.
- Recombination-proficient cells exhibited higher rates of trinucleotide repeat deletion compared to recombination-deficient cells.
- SOS system induction did not play a major role in trinucleotide repeat instability, and repeats did not trigger the SOS response.
Conclusions:
- Recombination proficiency is directly correlated with increased genetic instability in trinucleotide repeats.
- DNA repair mechanisms, particularly recombination, are critical in modulating trinucleotide repeat stability.
- A model suggesting replication restart attempts at paused triplet repeats as a mechanism for deletion during exponential growth is proposed.
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