@article{9455,
  abstract     = {Proteins of the ARGONAUTE family are important in diverse posttranscriptional RNA-mediated gene-silencing systems as well as in transcriptional gene silencing in Drosophila and fission yeast and in programmed DNA elimination in Tetrahymena. We cloned ARGONAUTE4 (AGO4) from a screen for mutants that suppress silencing of the Arabidopsis SUPERMAN(SUP) gene. The ago4-1 mutant reactivated silentSUP alleles and decreased CpNpG and asymmetric DNA methylation as well as histone H3 lysine-9 methylation. In addition,ago4-1 blocked histone and DNA methylation and the accumulation of 25-nucleotide small interfering RNAs (siRNAs) that correspond to the retroelement AtSN1. These results suggest that AGO4 and long siRNAs direct chromatin modifications, including histone methylation and non-CpG DNA methylation.},
  author       = {Zilberman, Daniel and Cao,  Xiaofeng and Jacobsen, Steven E.},
  issn         = {1095-9203},
  journal      = {Science},
  keywords     = {Multidisciplinary},
  number       = {5607},
  pages        = {716--719},
  publisher    = {American Association for the Advancement of Science},
  title        = {{ARGONAUTE4 control of locus-specific siRNA accumulation and DNA and histone methylation}},
  doi          = {10.1126/science.1079695},
  volume       = {299},
  year         = {2003},
}

@article{9495,
  abstract     = {RNA interference is a conserved process in which double-stranded RNA is processed into 21–25 nucleotide siRNAs that trigger posttranscriptional gene silencing. In addition, plants display a phenomenon termed RNA-directed DNA methylation (RdDM) in which DNA with sequence identity to silenced RNA is de novo methylated at its cytosine residues. This methylation is not only at canonical CpG sites but also at cytosines in CpNpG and asymmetric sequence contexts. In this report, we study the role of the DRM and CMT3 DNA methyltransferase genes in the initiation and maintenance of RdDM. Neither drm nor cmt3 mutants affected the maintenance of preestablished RNA-directed CpG methylation. However, drm mutants showed a nearly complete loss of asymmetric methylation and a partial loss of CpNpG methylation. The remaining asymmetric and CpNpG methylation was dependent on the activity of CMT3, showing that DRM and CMT3 act redundantly to maintain non-CpG methylation. These DNA methyltransferases appear to act downstream of siRNAs, since drm1 drm2 cmt3 triple mutants show a lack of non-CpG methylation but elevated levels of siRNAs. Finally, we demonstrate that DRM activity is required for the initial establishment of RdDM in all sequence contexts including CpG, CpNpG, and asymmetric sites.},
  author       = {Cao, Xiaofeng and Aufsatz, Werner and Zilberman, Daniel and Mette, M.Florian and Huang, Michael S. and Matzke, Marjori and Jacobsen, Steven E.},
  issn         = {1879-0445},
  journal      = {Current Biology},
  number       = {24},
  pages        = {2212--2217},
  publisher    = {Elsevier},
  title        = {{Role of the DRM and CMT3 methyltransferases in RNA-directed DNA methylation}},
  doi          = {10.1016/j.cub.2003.11.052},
  volume       = {13},
  year         = {2003},
}

@article{9444,
  abstract     = {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.},
  author       = {Lindroth, A. M. and Cao, Xiaofeng and Jackson, James P. and Zilberman, Daniel and McCallum, Claire M. and Henikoff, Steven and Jacobsen, Steven E.},
  issn         = {1095-9203},
  journal      = {Science},
  keywords     = {Multidisciplinary},
  number       = {5524},
  pages        = {2077--2080},
  publisher    = {American Association for the Advancement of Science},
  title        = {{Requirement of CHROMOMETHYLASE3 for maintenance of CpXpG methylation}},
  doi          = {10.1126/science.1059745},
  volume       = {292},
  year         = {2001},
}