"About 60% of human genes possess CpG islands near their promoters, whose methylation state is different in different tissues."
I understand what a CpG island is but what is the significance of them? And what is the significance of location near promoters?

Question

"About 60% of human genes possess CpG islands near their promoters, whose methylation state is different in different tissues."
I understand what a CpG island is but what is the significance of them? And what is the significance of location near promoters?

anonymous · Answer

I believe that the C's in CG pairs are what gets methylated, so you need such sites in order for methylation to (potentially) take place, and the more CG pairs you have then the more the methylation can have an effect. The fact that a site is methylated or not can affect gene transcription by affecting whether the transcription machinery can/will attach to the DNA at that point, so you would expect such regulatory CG rich sequences to be associated with promoters so they can effectively turn them "on" or "off" as appropriate in different tissues, or under different circumstances. Useful references: http://en.wikipedia.org/wiki/Epigenetics http://en.wikipedia.org/wiki/DNA_methylation http://en.wikipedia.org/wiki/CpG_site http://en.wikipedia.org/wiki/CpG_island Z.