DNA Methylation of the Endogenous PAI Genes in Arabidopsis

In eukaryotes, the association of genomic DNA withhistone proteins to form chromatin allows packaging ofDNA into the nucleus. However, the degree of chromatincompaction varies along the length of each chromosome,with some regions present in relatively open transcriptionally active euchromatin, and some regions present inmore compact transcriptionally silent heterochromatin.In particular, repetitive arrays associated with centromeres and ribosomal RNA-encoding genes (rDNA), aswell as transposable element sequences (both DNA transposons and retrotransposons), are assembled into heterochromatin. In the case of repeat arrays, heterochromatin is likely to serve as a means of stabilizing thesestructures against rearrangement, whereas in the case oftransposable elements heterochromatin serves as a meansof genome defense against deleterious effects of theirtranscription and movement. Thus, the integrity of chromatin organization is critical for correct patterns of geneexpression and genome stability. Key questions are howchromatin organization patterns are established, and howthese patterns are maintained through cell divisions...