Improving CRISPR-Cas9 Genome Editing Efficiency by Fusion with Chromatin-Modulating Peptides.

Bacterial-derived CRISPR-Cas9 nucleases have become a common tool in genome engineering. However, the editing efficiency by even the best-crafted Cas9 nucleases varies considerably with different genomic sites, and efforts to explore the vast natural Cas9 diversity have often met with mixed or little success. Here, we show that modification of the widely used Streptococcus pyogenes Cas9 by fusion with chromatin-modulating peptides (CMPs), derived from high mobility group proteins HMGN1 and HMGB1, histone H1, and chromatin remodeling complexes, improves its activity by up to several fold, particularly on refractory target sites. We further show that this CMP fusion strategy (termed CRISPR-chrom) is also effective in improving the activities of smaller Cas9 nucleases from Streptococcus pasteurianus and Campylobacter jejuni, as well as four newly characterized Cas9 orthologs from Bacillus smithii, Lactobacillus rhamnosus, Mycoplasma canis, and Parasutterella excrementihominis. Our findings suggest that this CRISPR-chrom strategy can be used to improve established Cas9 nucleases and facilitate exploration of novel Cas9 orthologs for genome modification.