CRISPR interference (CRISPRi) is a novel method for specific gene knockdown. It's CRISPR, without the cut. The Horizon CRISPRi system uses a deactivated Cas9 nuclease (dCas9) fused to our proprietary SALL1-SDS3 repressor construct to block transcription of target genes, without cutting the DNA.The Horizon CRISPRi system requires two components: a specialized dCas9 fused to repressor proteins (SALL1 and SDS3), and a guide RNA specifically designed to target the region immediately downstream of a gene’s transcriptional start site (TSS). The guide associates with dCas9-SALL1-SDS3 and directs the complex to the DNA target site. Horizon offers lentiviral and transient approaches for both repressor protein and guide introduction. The native Cas9 DNA-cutting functionality has been obliterated by point mutations, and the deactivated Cas9 (dCas9) protein has been further engineered for gene repression by fusing Horizon's proprietary SALL1 and SDS3 repressor domains. Horizon Discovery tested many repressor constructs before creating our dCas9-SALL1-SDS3 fusion. While many current CRISPRi systems rely on dCas9-KRAB variants (Gilbert et al.,2013,Yeo et al., 2018, Moghadam et al., 2020, Alerasool et al., 2020), our novel repressor, covalently linked to the dCas9 protein, further inhibits target gene transcription by recruiting proteins involved in chromatin remodeling and gene silencing (Alland et al. 2002). The result is a broadly functional repressor, turning gene expression down but not off. CRISPRi dCas9-SALL1-SDS3 is available as mRNA for transient expression or in lentiviral particles for creating a stable dCas9-SALL1-SDS3 expressing cell line.