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Mol. Cell. Biol., 10 1995, 5586-5597, Vol 15, No. 10
MJ Singer, BA Marcotte and EU Selker
Repeat-induced point mutation (RIP) is a process that efficiently detects
DNA duplications prior to meiosis in Neurospora crassa and peppers them
with G:C to A:T mutations. Cytosine methylation is typically associated
with sequences affected by RIP, and methylated cytosines are not limited to
CpG dinucleotides. We generated and characterized a collection of
methylated and unmethylated amRIP alleles to investigate the connection(s)
between DNA methylation and mutations by RIP. Alleles of am harboring 84 to
158 mutations in the 2.6-kb region that was duplicated were heavily
methylated and triggered de novo methylation when reintroduced into
vegetative N. crassa cells. Alleles containing 45 and 56 mutations were
methylated in the strains originally isolated but did not become methylated
when reintroduced into vegetative cells. This provides the first evidence
for de novo methylation in the sexual cycle and for a maintenance
methylation system in Neurospora cells. No methylation was detected in am
alleles containing 8 and 21 mutations. All mutations in the eight primary
alleles studied were either G to A or C to T, with respect to the coding
strand of the am gene, suggesting that RIP results in only one type of
mutation. We consider possibilities for how DNA methylation is triggered by
some sequences altered by RIP.
Copyright © 1995, American Society for Microbiology
DNA methylation associated with repeat-induced point mutation in Neurospora crassa
Institute of Molecular Biology, University of Oregon, Eugene 97403, USA.
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