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Illustration of Cas9 binding to DNA. The top figure shows two nucleosomes surrounding a nucleosome-free stretch of DNA. Hypothetical PAM sites for Cas9 targets in the central region and the right-hand nucleosome are shown in red. The lower figure shows Cas9 (with sgRNA) bound to the central target, with the PAM and flanking DNA held deep in the protein cleft. The PAM in the nucleosome could not be accessed without dissociating the DNA from the histone core. DNA backbones are blue; the RNA backbone is teal; DNA and RNA bases are white, except for the PAM; histones are green; Cas9 is purple. Credit: Janet Iwasa (University of Utah, Salt Lake City).
A team of researchers at the University of Utah has found that nucleosomes can inhibit CRISPR/Cas9 cleavage efficiency. In their paper published in Proceedings of the National Academy of Sciences, the group describes testing the gene editing technique on yeast samples and what they found.
Gene - Uses - RNA - Segments - DNA—but
The gene editing technique CRISPR-Cas 9 uses guide RNA to find and snip out segments of DNA—but what happens when the targeted segment is part of a nucleosome? Prior research has suggested that in such instances, it is likely that cleavage efficiency would suffer. In this new effort, the researchers have carried out an in vivo test of such instances and found that prior research results were correct—using CRISPR-Cas 9 on nucleosomes may not work very well.
DNA strands are tiny, but really long—approximately six feet long if stretched out. Because of that, cells have mechanisms for packing DNA into a cell nucleus. That mechanism involves rolling the strands into bunches around a given protein. Such rolled bunches are known as nucleosomes. Logic suggests that a technique for editing a strand of DNA might encounter difficulty because of accessibility issues. Other researchers have considered the possibility of...
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