User:SargasticSailor/sandbox

Unedited
RNA-directed DNA methylation (RdDM) is an epigenetic process first discovered in plants. During RdDM, double-stranded RNAs (dsRNAs) are processed to 21-24 nucleotide small interfering RNAs (siRNAs) and guide methylation of homologous DNA loci. In plants dsRNAs may be generated from four sources:


 * Viral replication intermediates
 * Products of the endogenous RNA-directed RNA polymerase
 * Transcribed inverted repeats
 * Transposable elements

Besides RNA molecules, a plethora of proteins are involved in the establishment of RdDM, like Argonautes, DNA methyltransferases, chromatin remodelling complexes. and the plant-specific Polymerase IV and Polymerase V. All these act in concert to add a methyl-group at the 5' position of cytosines. In contrast to animals, cytosines at all sequence context (CG, CHG, CHH) may get de novo methylated in plants.

Edited
= RNA-Directed DNA Methylation = RNA-directed DNA methylation (RdDM) is an epigenetic process that involves RNA interference (RNAi) within the nucleus of the cell. RdDM was first discovered in the plant Arabidopsis thaliana (A. thaliana), and later found to be in fungi and animals. A set of RNA molecules known as nuclear small RNAs are responsible for this transcriptional interference. These include small interfering RNAs (siRNAs), PIWI-interacting RNAs (piRNAs), and microRNAs (miRNAs). These fragments are approximately 20-30 base pairs long.