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Mechanistic Answer: It comes down to probability. Not every amino acid can be modified. H3 is the longest tail and it also has the highest density of amino acids that can be modified (e.g. AAs with nucleophilic functional groups like lysine). For example, H2A only has 7 possible sites whereas H3 has 21.
Why did it evolve this way? We don't know. I would guess that since H3 is associated with transcriptional control, it was advantageous to be able to regulate in a more complex/fine-tuned way.
Comment by inquilinekea at 14/04/2022 at 00:44 UTC
1 upvotes, 0 direct replies
Wow, and H3 is also the histone lost most with aging..