Compact type II-D Cas9 nucleases for efficient and specific genome editing

Compact type II-C Cas9 nucleases with expanded PAM access and high fidelity for therapeutic genome editing

Compact type II-C Cas9 nucleases are attractive for therapeutic genome editing because their small size enables packaging into adeno-associated viral (AAV) vectors, and their extended protospacer-adjacent motifs (PAMs) reduce off-target cleavage while expanding targeting scope. Yet characterized type II-C orthologs have edited mammalian cells far less efficiently than the canonical SpCas9. Here, we used embedding-based metagenomic mining of >4.7 × 10 proteins, combined with AlphaFold3 structure prediction and locus-context analysis, to identify three previously uncharacterized compact type II-C Cas9 orthologs, NsuCas9 (1,092 aa), PsuCas9 (1,084 aa), and GfoCas9 (1,074 aa), and benchmarked them in vitro and in human HEK293T cells. All three are robust RNA-guided nucleases with distinct PAM specificities (N CC, N NYAA, and N RHAA, respectively), divergent thermal profiles, and asymmetric sgRNA cross-compatibility. In human cells, PsuCas9 with an N ATAA PAM reaches 78.4% indels and matches or exceeds SpCas9 at multiple loci, representing the first natural compact type II-C ortholog reported to do so, while GfoCas9 and NsuCas9 add complementary coverage. All three show a strong deletion-biased repair signature and no detectable editing across 33 predicted off-target sites. These compact, high-fidelity nucleases expand the CRISPR targeting space for AAV-deliverable therapeutic editing.

Rational and computation-assisted engineering of a compact and efficient StaCas9 genome editor

flexiAsCas12a and other Cas12a variants enhance the applicability of Cas12a nucleases in prime editing

Amongst the genome manipulation tools based on the versatile CRISPR-Cas system, prime editing is the most prominent one as a method that enables precise insertions, deletions, and substitutions without inducing double-strand breaks. Cas12a nucleases are widely used for genome editing and nucleic acid detection, owing to their unique properties; however, their relatively long PAM requirements limit their applicability. We develop PAM-flexible Cas12a variants capable of functioning effectively within mammalian cells, thereby enabling the cleavage of targets previously inaccessible to Cas12a nucleases. Amongst the Lb-, As-, Mb-, and FnCas12a variants we develop, flexiAsCas12a (AsCas12a with flexible PAM recognition) is the most effective, expanding the range of recognized PAM sequences by Cas12a variants to include NATN, NCCN and GTCN sequences. Using the currently available Cas12a variants with relaxed PAM recognition (impLbCas12a, flexiAsCas12a, and enAsCas12a), we develop circular RNA-guided split prime editors and validate their functionality on non-canonical PAM sequences. flexiAsCas12a joins the repertoire of Cas12a PAM variants, enabling access to an increasing number of target sequences by Cas12a nucleases.

Compact 9dBEs Enable Efficient and Precise Genome Editing in Mammalian Cells and In Vivo

An efficient Cas9d system (Cas9dUltra) is developed through gRNA and protein engineering, and its base editors (9dBEs) further developed through gRNA and protein engineering, enabling efficient and precise genome editing in human cells.

Shared CRISPR arrays underpin type I-A/I-B coexistence.

CRISPR-Cas systems provide adaptive immunity in prokaryotes, yet how multiple CRISPR-Cas subtypes coexist and coordinate within a single genome remains unclear. Comparative genomic analysis revealed that nearly one-third of type I-A CRISPR-Cas3 systems are adjacent to a type I-B system, often sharing a single CRISPR array. Using Thermococcus siculi RG-20 (Tsi) as a model, we show that purified TsiCas6a and TsiCas6b independently recognize and cleave the shared pre-crRNA, producing mature crRNAs with comparable efficiency. Plasmid interference assays further demonstrated that crRNAs produced by either Cas6a or Cas6b enzyme could guide both type I-A and type I-B interference complexes. This interchangeability shows that crRNAs generated by either Cas6a or Cas6b can be loaded into, and function with, both type I-A and type I-B interference complexes. Structural modelling revealed distinct but complementary recognition strategies for Cas6a and Cas6b, and mutational analysis of their RNA-binding residues impaired pre-crRNA cleavage and abolished interference activity. Together, these results uncover a shared-array logic in which Cas6a/Cas6b-compatible processing routes a single pre-crRNA to multiple type I effectors-providing a potential mechanism for subtype co-existence, a plausible explanation for array-less (or "orphan") interference modules, and an evolutionary bet-hedging strategy that prevents Acrs from shutting down immunity wholesale.

A Novel, Simple, and Highly Efficient Dual-sgRNA CRISPR/Cas9-Based Editing System in the Filamentous Fungus Fusarium oxysporum

Fusarium oxysporum, as one of the most common filamentous fungi, possesses great biosynthetic potential for natural products. However, the lack of efficient genetic tools has hindered functional genome mining and metabolic engineering in this fungus. In this study, a novel highly efficient CRISPR/Cas9-based dual-sgRNA expression editing system for F. oxysporum was successfully developed through construction of a robust plasmid platform pFRCas9-G418 using incorporation of an endogenous histone H2B nuclear localization signal and a 5S rRNA promoter-driven polycistronic tRNA−sgRNA cassette. This system is suitable not only for single-gene editing but also for large-fragment deletion and multiplex gene editing, although the editing efficiency is somewhat lower. First, this new CRISPR/Cas9 system exhibited a high efficiency of 93.75% ± 6.25% for deletion of the Fusarium cyclin C1 (fcc1) gene (∼1 kb), which was usually selected as the target gene responsible for yellow pigment accumulation. Then, knockout of the core NRPS gene sanB (∼19 kb) and knock-in of the strong promoter gpdA in the N-methylsansalvamide (SA) biosynthetic gene cluster (BGC) in strain F. oxysporum R1 using this system, respectively, led to no SA yield and an increase of 26.4% SA titer, confirming its capacity for large gene deletion and gene knock-in. Furthermore, one-step dual-gene knockout of hat1 (histone acetyltransferase gene, ∼1.5 kb) and pacC (pH-responsive transcription factor, ∼2 kb) was first achieved in Fusarium species. This versatile platform provides a powerful tool for editing gene(s) of various sizes in F. oxysporum.