Genome complexity: controlling epigenetic marks (Introduction)

by David Turell @, Tuesday, June 30, 2020, 22:18 (12 days ago) @ David Turell

A mechanism in plants is described:

"Epigenetic regulation of gene expression is associated with switching between chromatin states characterized by distinct histone modifications.

"...researchers characterized a gene from an early flowering Arabidopsis mutant and showed that the mutated gene encodes a protein that modifies chromatin—that is it affects the chemical modifications of the histone proteins that surround the DNA in our cells. This class of modifier had not been well characterized in plants before.

"Further, they find that the modifier protein physically associates with a well-known class of chromatin modifiers—called Polycomb proteins.

"Polycomb proteins add an epigenetic mark (methylation) at a specific point (lysine residue at position 27) in the amino acid sequence of a histone protein that packages the DNA and this leads to silent chromatin.

"The addition of this epigenetic mark can only happen when another nearby site (lysine residue at position 36) in the amino acid sequence is not modified. They are mutually exclusive- that is only one of these specific sites can be modified with the epigenetic mark at any one time.

"Interestingly, the newly discovered modifier protein facilitates removal of the epigenetic mark at lysine 36, thus allows Polycomb to add the epigenetic mark at lysine 27. The physical association of the two activities helps generate a switch of active chromatin to silent chromatin."

Comment: this shows how specific histone proteins add and remove methylation markers while DNA is wound around histones. This complexity requires a designer.

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