"CRISPR is a tool to help scientists modify the genome, predict the outcome of certain traits and study them, but the tool itself only creates breaks in the genome. It does not control how a new DNA sequence is inserted into the genome," says Geraldine Seydoux, Ph.D., the Huntington Sheldon Professor in Medical Discovery in the Department of Molecular Biology and Genetics and vice dean for basic research at the Johns Hopkins University School of Medicine, and an investigator with the Howard Hughes Medical Institute.
"We set out to study how cells repair breaks induced by CRISPR with the goal of using the cell's natural DNA repair process to introduce new sequences in the genome. We were surprised to find that cells will readily copy sequences from foreign DNA to repair DNA breaks, as long as the foreign DNAs are linear," Seydoux adds. "By studying how foreign DNA fragments are copied during the repair process, we came up with some simple rules to make genome editing as efficient as possible, optimize the tool, and do so with confidence."
CRISPR, which stands for clustered regularly interspaced short palindromic repeat, has gained popularity among scientists in the last five years as a tool to efficiently cut DNA. It was adapted for use in mammalian cells from a natural viral defense process in bacterial cells that involves creating lethal cuts in viral DNA. Essentially, the tool is a streamlined set of molecular "scissors."
The prevailing belief, among scientists, is that cells repair DNA breaks by inserting a random set of nucleotides, the chemical building blocks of DNA. This usually destroys any gene that's located at the spot where the DNA is broken.
https://phys.org/news/2017-12-scientists-efficiency-gene-technology.html
