GOLD gRNA - allows robust genome editing regardless of spacer sequence composition by super stable hairpin technology

A Cas nuclease such as Cas9 can introduce a DNA double strand break in a sequence target that is complementary to a 20-nt spacer sequence of its bound guide RNA (gRNA) when a protospacer adjacent motif (PAM) is present. The gRNA can be provided as duplex of spacer containing CRISPR RNA (crRNA) and trans-activating crRNA (tracrRNA). Or as a single gRNA (sgRNA) where crRNA and tracrRNA are fused by an artificial loop.
Hence a gRNA consists of the target-specific spacer and a constant part typically comprised of distinct motifs including the nexus, and a first and second hairpin.
Genome editing efficiencies vary strongly from sequence target to sequence target and some sequence targets are totally intractable to genome editing. This results in a need to pre-screen several gRNAs to find an efficient one. In addition numerous gRNA efficiency algorithms have been employed to allow in-silico prescreening. But their accuracy is far from satisfying.
Investigation of certain biological questions or precise repair of disease alleles can be prevented or limited to the use of a potentially inefficient single target site. Or large scale Crispr screens could not be harnessed with optimally covering gRNA libraries.