title: Atypical RNA polymerase subunits required for RNA-directed DNA methylation.
abstract: RNA-directed DNA methylation, one of several RNA interference-mediated pathways in the nucleus, has been documented in plants and in human cells. Despite progress in identifying the DNA methyltransferases, histone-modifying enzymes and RNA interference proteins needed for RNA-directed DNA methylation, 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 groups. DRD1 is a SNF2-like protein 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 silencing. 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.
authors.affiliation: Gregor Mendel Institute of Molecular Plant Biology, Austrian Academy of Sciences, UZA2, Pharmazie Zentrum, Althanstrasse 14/2D-541, A-1090 Vienna, Austria.
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Kanno
authors.forename: Bruno
authors.initials: B
authors.lastname: Huettel
authors.forename: M Florian
authors.initials: MF
authors.lastname: Mette
authors.forename: Werner
authors.initials: W
authors.lastname: Aufsatz
authors.forename: Estelle
authors.initials: E
authors.lastname: Jaligot
authors.forename: Lucia
authors.initials: L
authors.lastname: Daxinger
authors.forename: David P
authors.initials: DP
authors.lastname: Kreil
authors.forename: Marjori
authors.initials: M
authors.lastname: Matzke
authors.forename: Antonius J M
authors.initials: AJ
authors.lastname: Matzke
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D019175:DNA Methylation; D012321:DNA-Directed RNA Polymerases / Q000235:genetics / Q000378:metabolism*; D020868:Gene Silencing; D008969:Molecular Sequence Data; D009154:Mutation; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism*
chemical_list: D021122:Protein Subunits; D018749:RNA, Plant; C499181:RNA polymerase IV, Arabidopsis; D012321:DNA-Directed RNA Polymerases