The Broad Institute of MIT and Harvard and the McGovern Institute for Brain Research at MIT researchers have designed and built alterations to the revolutionary CRISPR-Cas9 genome editing system that notably cut down on ‘off-target’ editing errors. The refined technique deals with one of the key technical problems in the use of genome editing.

The CRISPR-Cas9 system functions by bringing an accurately targeted alteration in the DNA of a cell. The protein Cas9 changes the DNA at an area that is specified by a small RNA, with sequence matching the one of the target site.

Though Cas9 is called highly proficient at cutting its target site, the systems main drawback has been that it can attach to and cut extra sites that are not targeted, once it is inside a cell.

It has the capability to come up with undesired edits, changing gene expression or knock a gene out completely, which could result into cancer development or other issues.

In a paper published recently in Science, Feng Zhang along with his colleagues have reported that alteration of three of roughly 1,400 amino acids that create the Cas9 enzyme from S. pyogenes spectacularly decreased ‘off-target editing’ to untraceable levels in the examined specific cases.

Zhang and his colleagues gained knowledge regarding the Cas9 protein’s structure and then they decreased off-target cutting. DNA is negatively charged and it attaches to a groove in the Cas9 protein, having positively charged.

Knowledge about structure made scientists capable of predicting that replacement of some of the positively charged amino acids with neutral ones would cut the binding of ‘off target’ sequences quite more as compared to ‘on target’ sequences.

Zhang's team did experiments with many likely changes and discovered that mutations in three amino acids noticeably decreased ‘off-target’ cuts.