CRISPR-Cas9 is a CRISPR-Cas gene editing system that uses the Cas-9 protein to cut the double-stranded DNA at specific sites. CRISPR-Cas9 was adapted from a naturally occurring genome editing system that is part of a bacteria’s immune defense (Streptococcus bacteria). Cas9 is only one of many different RNA-guided nucleases in bacterial genomes.
U.S. National Library of Medicine (NLM) MedlinePlus: What are genome editing and CRISPR-Cas9?
Wellcome Genome Campus YourGenome: What is CRISPR-Cas9?
NCATS Toolkit for Patient-Focused Therapy Development: Genetic Therapeutics