Remarkably Long-Tract Gene Conversion Induced by Fragile Site Instability in Saccharomyces cerevisiae.
Shahana A Chumki1, Mikael K Dunn1, Thomas F Coates1
1Department of Biology, Eastern Michigan University, Ypsilanti, Michigan 48197.
Genetics
|June 26, 2016
Summary
Replication stress drives gene conversion at fragile sites. Break-induced replication (BIR) is a key mechanism promoting loss of heterozygosity (LOH) at common fragile sites, impacting human tumors.
Area of Science:
- Genetics
- Molecular Biology
- Cancer Research
Background:
- Replication stress induces breaks at common fragile sites (CFS).
- Loss of heterozygosity (LOH) in tumors correlates with CFS, but gene conversion's role is unclear.
- Investigating gene conversion mechanisms at CFS is crucial for understanding LOH in cancer.
Purpose of the Study:
- To investigate gene conversion stimulated by instability at fragile site FS2 in Saccharomyces cerevisiae.
- To determine the mechanisms and characteristics of gene conversion during LOH at CFS.
- To assess the contribution of different DNA repair pathways to LOH at fragile sites.
Main Methods:
- Utilized a yeast (Saccharomyces cerevisiae) screening system to identify mitotic LOH events near fragile site FS2.
- Analyzed single nucleotide polymorphisms (SNPs) between homologs to determine LOH cause and extent.
- Characterized gene conversion tract lengths and crossover association.
Main Results:
- Fragile site FS2 instability increased gene conversion 48- to 62-fold.
- Conversions unassociated with crossover constituted 6-7% of LOH events.
- Bidirectional gene conversion tracts at FS2 averaged 40.8 kb, suggesting prominent break-induced replication (BIR) as a repair mechanism.
Conclusions:
- Break-induced replication (BIR) is a major mechanism for repairing lesions at fragile sites.
- BIR-driven gene conversion contributes significantly to common fragile site-stimulated LOH in human tumors.
- Understanding these mechanisms can inform cancer diagnostics and therapeutics.
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