Covalent modifications of histone-tail amino acid residues communicate information via a specific 'histone code'. Here, we report histone H3-tail lysine methylation profiles of several Arabidopsis genes in correlation with their transcriptional activity and the input of the epigenetic factor ARABIDOPSIS HOMOLOG OF TRITHORAX (ATX1) at ATX1-regulated loci. By chromatin immunoprecipitation (ChIP) assays, we compared modification patterns of a constitutively expressed housekeeping gene, of a tissue-specific gene, and among genes that differed in degrees of transcriptional activity. Our results suggest that the di-methylated isoform of histone H3-lysine4 (m2K4/H3) provide a general mark for gene-related sequences distinguishing them from non-transcribed regions. Lys-4 (K4/H3), lys-9 (K9/H3) and lys-27 (K27/H3) nucleosome methylation patterns of plant genes may be gene-, tissue- or development-regulated. Absence of nucleosomes from the LTP-promotor was not sufficient to provoke robust transcription in mutant atx1-leaf chromatin, suggesting that the mechanism repositioning nucleosomes at transition to flowering functioned independently of ATX1.
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