Nature Genetics37, 761 - 765 (2005)
Published online: 29 May 2005; | doi:10.1038/ng1580
Atypical RNA polymerase subunits required for RNA-directed DNA methylation
Tatsuo Kanno1, Bruno Huettel1, M Florian Mette1, 3, Werner Aufsatz1, Estelle Jaligot1, Lucia Daxinger1, David P Kreil2, Marjori Matzke1
& Antonius J M Matzke1
1
Gregor Mendel Institute of Molecular Plant Biology, Austrian Academy of Sciences, UZA2, Pharmazie Zentrum, Althanstrasse 14/2D-541, A-1090 Vienna, Austria.
2
WWTF Vienna Science Chair of Bioinformatics, Department of Biotechnology c/o IAM, Muthgasse 18, A-1190 Vienna, Austria.
RNA-directed DNA methylation, one of several RNA interference−mediated pathways in the nucleus1, has been documented in plants2,
3 and in human cells4,
5. Despite progress in identifying the DNA methyltransferases, histone-modifying enzymes and RNA interference proteins needed for RNA-directed DNA methylation1, the mechanism remains incompletely understood. We screened for mutants defective in RNA-directed DNA methylation and silencing of a transgene promoter in Arabidopsis thaliana and identified three drd complementation groups6. DRD1 is a SNF2-like protein6 required for RNA-directed de novo methylation. We report here that DRD2 and DRD3 correspond to the second-largest subunit and largest subunit, respectively, of a fourth class of DNA-dependent RNA polymerase (polymerase IV) that is unique to plants. DRD3 is a functionally diversified homolog of NRPD1a or SDE4, identified in a separate screen for mutants defective in post-transcriptional gene silencing7,
8. The identical DNA methylation patterns observed in all three drd mutants suggest that DRD proteins cooperate to create a substrate for RNA-directed de novo methylation.
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