Crispr/Cas9 is a riboprotein complex composed of a short strand of RNA and an efficient DNA-cutting enzyme. Crispr/Cas9 sometimes cuts in the wrong places. And it has no off-switch.
Other proteins—like ones that activate gene expression—can be combined with a crippled Cas9, letting them toggle genes on and off (sometimes with light or chemical signals) without altering the DNA sequence. Epigenetic editing could be used to tackle conditions such as diabetes, acute kidney disease, and muscular dystrophy.
Editing individual base pairs
Crispr system has been modified to edit individual base pairs, one at a time. They designed a brand-new enzyme—one not found in nature—that could chemically convert an A-T nucleotide pairing to a G-C one. David Liu, the Harvard chemist whose lab did the work, estimates that about half of the 32,000 known pathogenic point mutations in humans could be fixed by that single swap.
Creating programmable off switches for Crispr
Researchers have identified 21 unique families of naturally occurring anti-Crispr proteins—small molecules that turn off the gene-editor. But they only know how a handful of them work. Some bind directly to Cas9, preventing it from attaching to DNA. Others turn on enzymes that outjostle Cas9 for space on the genome. Researchers at UC Berkeley, UCSF, Harvard, the Broad, and the University of Toronto are hard at work figuring out how to turn these natural off-switches into programmable toggles.
Cas editing of RNA instead of DNA
Crispr co-discoverer Feng Zhang are working with a new class of Cas enzymes that target RNA instead of DNA. RNA are the instructions that a cell’s machinery reads to build proteins. RNA would be useful for treating short-term problems like acute inflammation or wounds. The system is called calling Repair (RNA Editing for Programmable A to I Replacement). It currently works for one nucleotide conversion. The next step is to figure out how to do the other 11 possible combinations.
Many Cas cutting enzymes
There are many cutting enzymes beyond Cas9. There is cpf1, CasX and CasY. Many more will be developed.
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