Distribution of H3K4me in the Arabidopsis genome. (a) Chromosomal distribution of H3K4me. Top row: the total length of repetitive sequences (y-axis, left-side scale) and number of genes per 100 kb (y-axis, right-side scale). Bottom panels: chromosomal distribution of H3K4me1, H3K4me2 and H3K4me3. X-axis: chromosomal position; y-axis: the total length of genomic regions containing H3K4me1, H3K4me2 and H3K4me3 per 100 kb, respectively. Arrows indicate the heterochromatic knob on chromosome 4. (b) Local distribution of H3K4me1, H3K4me2, H3K4me3, other epigenetic marks (DNA methylation, H3K9me2, H3K27me3, nucleosome density, small RNAs) and transcription activity in an approximately 40-kb euchromatic region on chromosome 1. Repetitive sequences are shown as filled red boxes on top. Individual genes are shown in open red boxes (arrows indicate direction of transcription; filled light blue boxes, exons; light blue lines, introns). Distribution of H3K4me on the gene labeled by a red asterisk is enlarged and shown in detail at the bottom.