Biological complexity: how cells read-write their DNA (Introduction)

by David Turell , Tuesday, November 07, 2023, 20:20 (171 days ago) @ David Turell

Finally unraveled:

https://phys.org/news/2023-11-cell-readwrite-mechanism-uncover-gene.html

"'Whether histone modifications are the epigenetic cause for gene expression has remained a hypothesis because no one had ever seen whether histone modifications self-replicate," explains Takashi Umehara of the RIKEN Center for Biosystems Dynamics Research.

"To explore this question, Umehara and his team focused on a protein known as p300/CBP—an enzyme that can both introduce and bind to acetyl-group modifications (acetylations) on histone proteins. Specifically, the researchers were interested in specific acetylations on the histone H3–H4 complex to which p300/CBP binds. These acetylations are known to activate gene expression in nearby DNA sequences.

"But H3–H4 is just one component of a larger "nucleosome" assembly, which also includes the histone H2B–H2A complex. All of these various histones can carry distinct acetylation patterns, and the causal relationships between their acetylations have not been well understood.

***

"The team found that p300/CBP recognizes and binds to specific acetylation marks on the H3–H4 complex. The enzyme then replicates acetylation marks to unacetylated sites of H3–H4, while also transcribing them from H3–H4 to H2B–H2A within the same nucleosome. Since this newly acetylated H2B–H2A complex is more likely to be stripped from the nucleosome, a model emerges in which it finally instructs which genes to be transcribed by the cellular transcription machinery.

"These results provide an unprecedented glimpse into how p300/CBP inherits acetylation marks to newly divided cells and utilizes those marks epigenetically for gene expression. "I could never have imagined such an elegant yin–yang mechanism for the inheritance and expression of epigenetic information," says Umehara."

Comment: another example of design in evolution. Each step must be coordinated between the necessary molecules. Irreducible complexity again.