DUSP11 is an RNA triphosphatase that limits <i>Psp</i> Cas13b activity by destabilizing gRNA abundance in mammalian cells

The CRISPR-Cas13 system enables programmable RNA targeting with potential applications in therapeutics and research. However, while PspCas13b mediates efficient RNA knockdown following transient transfection, stable lentiviral delivery results in minimal activity, limiting its utility. Here, we performed a genome-wide CRISPR-Cas9 knockout screen to identify mammalian factors that restrict PspCas13b activity. We discovered that DUSP11, an RNA triphosphatase, suppresses PspCas13b function by dephosphorylating the 5'-triphosphate of Pol III-transcribed guide RNAs (gRNAs), triggering their degradation. DUSP11 knockout increased gRNA levels 2.5-4-fold and enhanced PspCas13b-mediated knockdown across multiple cell lines. This enhancement was sustained for at least 27 days and enabled targeting of endogenous transcripts previously refractory to PspCas13b. Our findings reveal an unexpected host restriction of bacterial CRISPR systems and demonstrate that gRNA levels are a limiting factor. We provide a simple strategy to improve PspCas13b activity in mammalian cells. These results have implications for developing PspCas13b-based therapeutics and suggest that systematic identification of host factors regulating CRISPR components could enhance genome editing technologies.