Guide RNA engineering enables efficient CRISPR editing with a miniature Syntrophomonas palmitatica Cas12f1 nuclease

Gene therapy is limited by inefficient delivery of large clustered regularly interspaced short palindromic repeat (CRISPR) effectors, such as Cas9 and Cas12a nucleases. Cas12f nucleases are currently one of the most compact CRISPR genome editors. However, the available toolkit of efficient Cas12f editors is limited. Here, we report the characterization and engineering of a miniature CRISPR-Cas12f system from Syntrophomonas palmitatica (SpaCas12f1, 497 amino acids). We show that CRISPR-SpaCas12f1 cleaves double-stranded DNA (dsDNA) with 5' T-rich PAM specificity and is naturally active for genome editing in bacteria. We identify that CRISPR-SpaCas12f1 trans-activating CRISPR RNA (tracrRNA) harbors a unique head-to-toe hairpin structure, and the natural hairpin structure is a key factor in restricting genome editing by SpaCas12f1 in human cells. Systematical engineering of SpaCas12f1 guide RNA transforms CRISPR-SpaCas12f1 into an efficient genome editor comparable to Francisella novicida CRISPR-Cas12a. Our findings expand the mini CRISPR toolbox, paving the way for therapeutic applications of CRISPR-SpaCas12f1 and engineering compact genome manipulation technologies.