Farnung lab uncovers mechanism of nucleosome retention during transcription
Human genomic DNA is over 2 meters in length, but needs to be compacted to fit into the tight confinements of the cell’s nucleus that has a size of ~5 µm. This is achieved by wrapping the DNA tightly around histone proteins to form nucleosomes. These nucleosomes, however, form a barrier to RNA polymerase II, a molecular machine that is responsible for the transcription of most protein-coding genes in eukaryotes. How RNA polymerase II traverses nucleosomes without disrupting them is unknown.
In a study published in Science, the Farnung lab has now captured an intermediate of RNA polymerase II traversal through a nucleosome. The intermediate reveals a novel state where already transcribed DNA rewraps the nucleosome to stabilize it. This rewrapping has not been observed previously and presents an important milestone to understand how RNA polymerase II and other molecular machines move through chromatin without losing nucleosomes and associated epigenetic information.
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