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Mutations in yeast replication proteins that increase CAG/CTG expansions also increase repeat fragility
Julie L Callahan1, Kenneth J Andrews, Virginia A Zakian
1Department of Biology, Program in Genetics, Tufts University, Medford, Massachusetts 02155, USA.
Molecular and Cellular Biology
|October 16, 2003
Summary
Faulty DNA replication processes, particularly during Okazaki fragment maturation, can lead to trinucleotide repeat (TNR) instability and breakage. These DNA replication errors are linked to TNR expansions, a cause of genetic diseases.
Area of Science:
- Genetics
- Molecular Biology
- Genomic Instability
Background:
- Trinucleotide repeat (TNR) expansions are key mutations in numerous human genetic disorders.
- Expanded TNR tracts exhibit both instability (length changes) and fragility (breakage).
Purpose of the Study:
- To investigate the link between lagging-strand replication fidelity and TNR stability/fragility.
- To analyze CAG/CTG tract fragility in yeast mutants with defects in lagging-strand replication proteins.
Main Methods:
- Development of a novel yeast artificial chromosome (YAC)-based assay for chromosome breakage.
- Analysis of fragility in CAG/CTG tracts in mutants deficient for key lagging-strand replication proteins (Fen1/Rad27, Dna2, RNase HI, DNA ligase, polymerase delta, primase).
Main Results:
- RAD27 deletion significantly increased breakage in both short and long CAG/CTG tracts.
- Defects in DNA ligase and primase elevated breakage in long tracts.
- A correlation was observed between mutations increasing CAG/CTG tract breakage and those increasing repeat expansion.
Conclusions:
- Faulty Okazaki fragment processing and DNA repair mechanisms contribute significantly to TNR expansions.
- Strand break generation during replication is a critical source of TNR instability and disease-causing mutations.