Requirement of CHROMOMETHYLASE3 for Maintenance of CpXpG Methylation

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Science  15 Jun 2001:
Vol. 292, Issue 5524, pp. 2077-2080
DOI: 10.1126/science.1059745

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Epigenetic silenced alleles of the Arabidopsis SUPERMANlocus (the clark kent alleles) are associated with dense hypermethylation at noncanonical cytosines (CpXpG and asymmetric sites, where X = A, T, C, or G). A genetic screen for suppressors of a hypermethylated clark kent mutant identified nine loss-of-function alleles of CHROMOMETHYLASE3(CMT3), a novel cytosine methyltransferase homolog. These cmt3 mutants display a wild-type morphology but exhibit decreased CpXpG methylation of the SUP gene and of other sequences throughout the genome. They also show reactivated expression of endogenous retrotransposon sequences. These results show that a non-CpG DNA methyltransferase is responsible for maintaining epigenetic gene silencing.

  • * These authors contributed equally to this work.

  • To whom correspondence should be addressed. E-mail: jacobsen{at}

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