A link between H3K27me3 mark and exon length in the gene promoters of pluripotent and differentiated cells.

We conducted a reanalysis of genome-wide histone H3 tail methylation data in mammalian pluripotent and differentiated cells. We show that the promoters marked with histone H3 lysine 27 trimethylation (H3K27me3) tend to have more exonic positions in the promoter regions. However, this is not due to any preferential marking on exons over introns by H3K27me3. The relationship is also independent the status of histone H3 lysine 4 trimethylation (H3K4me3) mark, CpG content and the platforms used in the high-throughput profiling of histone modifications. It provides evidence for the link between histone modifications and transcribed exons in promoter regions.