| Eukaryotic genomes contain hundreds to thousands of repeated ribosomal RNA (rRNA) genes located within the nucleolus organizer regions (NOR). The level of rRNA gene transcription from these repeats is controlled by both the rate of transcription at each rRNA gene and the number of "open" rRNA genes available for transcription. Enzymes that alter chromatin modifications including histone acetylation, DNA methylation and nucleosome positioning influence rRNA gene expression. In Arabidopsis, RPD3-like historic deacetylase, HDA6, has been shown to regulate the transcription of the silent class of rRNA genes in the hybrid species of Arabidopsis, A. suecica. The experiments described within further our understanding of the mechanisms by which HDA6 regulates rRNA gene transcription in both hybrid and non-hybrid species of Arabidopsis. The data presented suggest that HDA6 is a broad specificity, Trichostatin A sensitive histone deacetylase that regulates transcription of silent rRNA genes in A. suecica. HDA6 localizes to the nucleolus, the site of rRNA gene transcription, where it may interact directly with the rRNA genes to deacetylate histories associated with the silent rRNA genes. The data suggest that HDA6, through its ability to deacetylate histones, regulates the number of "open" genes in non-hybrid species of Arabidopsis and controls spurious rRNA gene transcription within the intergenic spacer region between rRNA gene repeats. |
