Most of the human genes are found to be highly methylated in their 3'UTR region (0.8-0.9%). I was wondering if there is any specific reason for this?
According to Choi et al. Genome Biology 2009, 10:R89, DNA methylation at both coding boundaries may regulate transcription elongation and stabilize splicing by reducing the occurrences of exon skipping.
From the abstract:
Here we report a genome-wide observation of distinct peaks of nucleosomes and methylation at both ends of a protein coding unit. Elongating polymerases tend to pause near both coding ends immediately upstream of the epigenetic peaks, causing a significant reduction in elongation efficiency. Conserved features in underlying protein coding sequences seem to dictate their evolutionary conservation across multiple species. The nucleosomal and methylation marks are commonly associated with high sequence-encoded DNA-bending propensity but differentially with CpG density. As the gene grows longer, the epigenetic codes seem to be shifted from variable inner sequences toward boundary regions, rendering the peaks more prominent in higher organisms.
Their data (figures 1 and S2), however, do not support a generalized increase in the 3' UTR regions in either human T cells, mouse liver, yeast or flies.