The CRISPR-Cas9 system has been extensively researched due to its potential therapeutic use.Unfortunately, limitations concerning the number of locations on the genome it may encompass still constitute its major weakness.Scientists at the Massachusetts Institute of Technology have identified a new Cas9 enzyme which, in their view, may contribute to greater effectiveness to be potentially achieved by CRISPR.
CRISPR requires so-called PAM sequences to identify a specific DNA fragment to be cut. Without PAM, the editing cannot be carried out.However, the commonly-used Cas9 enzyme (StreptococcuspyogenesCas 9, in short referred to as SpCas9) only identifies those nucleotides that are followed by two G nucleotides as its PAM.This considerably limits the number of locations that CRISPR can reach - approximately, to 9.9% (estimates by the MIT researchers).
Scientists had used computational algorithms to scan bacterial sequences for enzymes demonstrating less restrictive requirements. Afterwards, their synthetic versions were built, with CRISPR taken into account.The so-called ScCas9 distinguished itself as the most successful one.While it is nearly identical to SpCas9, it demonstrates considerably greater efficiency, as it only needs one G nucleobase as its PAM, not two of them.Researchers at the MIT hope that their new CRISPR tool can help improve the accuracy of genome editing and increase the number of its applications.