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DNA methylation associated with repeat-induced point mutation in Neurospora crassa
M J Singer1, B A Marcotte, E U Selker
1Institute of Molecular Biology, University of Oregon, Eugene 97403, USA.
Molecular and Cellular Biology
|October 1, 1995
Summary
Repeat-induced point mutation (RIP) in Neurospora crassa causes G:C to A:T mutations. This study links DNA methylation to RIP, revealing de novo methylation during the sexual cycle and maintenance methylation.
Area of Science:
- Molecular Biology
- Genetics
- Epigenetics
Background:
- Repeat-induced point mutation (RIP) is a DNA repair mechanism in Neurospora crassa that targets duplicated sequences before meiosis.
- Cytosine methylation is often observed in RIP-affected regions, extending beyond CpG dinucleotides.
Purpose of the Study:
- To investigate the relationship between DNA methylation and RIP by analyzing methylated and unmethylated amRIP alleles.
- To understand the role of methylation in the RIP process and its regulation.
Main Methods:
- Generation and characterization of various amRIP alleles with differing mutation loads.
- Analysis of DNA methylation patterns in these alleles within Neurospora crassa strains.
- Assessment of de novo and maintenance methylation upon reintroduction of alleles.
Main Results:
- Alleles with high mutation counts (84-158) were heavily methylated and induced de novo methylation.
- Alleles with moderate mutation counts (45-56) showed existing methylation but no de novo induction.
- Low mutation count alleles (8-21) lacked detectable methylation.
- All observed mutations were G:C to A:T, indicating a single mutation type in RIP.
Conclusions:
- Provides the first evidence for de novo methylation during the sexual cycle in Neurospora.
- Demonstrates a DNA methylation maintenance system in Neurospora cells.
- Suggests a link between RIP-induced sequence alterations and the triggering of DNA methylation.