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> Methylating histones:
> 
> https://www.sciencedaily.com/releases/2024/09/240910121012.htm
> 
> "One of the most fascinating discoveries in biology is that cells have mechanisms for dynamically regulating genetic expression. This ability to promote or restrict the transcription of specific genes without altering the DNA sequences themselves is essential to all forms of life, from single-cell organisms to the most complex plants and animal species.
> 
> "While our understanding of these so-called epigenetic mechanisms is far from complete, remarkable progress has been made in this field with the understanding of the role of the Polycomb Repressive Complex 2 (PRC2). PRC2 is a protein that, in many plants, binds to specific DNA sequences called polycomb response elements (PREs) and applies a chemical mark to nearby histones (the structural support of DNA in the nucleus). Known as "trimethylation of H3K27 (H3K27me3)," this chemical modification prevents nearby genes from being converted into RNA and, in turn, into proteins, effectively silencing them. Despite this knowledge, however, scientists haven't yet understood how genes silenced by PRC2 can be turned back on.
> 
> ***
> 
> "After an extensive series of analyses and measurements on mutant A. Thaliana cultures, the researchers uncovered a new role for SDG7. It turns out this protein also binds to PREs, competing with PRC2. Moreover, SDG7 can actually displace PRC2, preventing it from leaving the H3K27me3 mark. On top of this, SDG7 adds an active histone mark itself via the methylation of H3K36. After H3K36 methylation is in place, the protein pair SDG8 and Polymerase Associated Factor 1 (PAF1) spread this active mark across the gene's body, resulting in efficient gene activation.
> 
> "In a way, the histone sites H3K27 and H3K36 can be interpreted as a "switch" that can dynamically turn on and turn off the expression of specific genes. "This simple and elegant antagonistic molecular switch between H3K27 and H3K36 methylation is ideally suited for epigenetic reprogramming during plant development," highlights Yamaguchi. "Since switching between H3K27 and H3K36 methylation has been seen in many flowering plants, the competitive mechanism between SDGs and PRC2 at PREs may be conserved across many plant species during for controlling development.'"
> 
> Comment: such a specific set of proteins indicate design. An on/off switch that dosn't damage DNA is elegant.