Multi-locus CRISPRi targeting with a single truncated guide RNA [RNA-seq]
A critical goal in functional genomicsis evaluating which non-coding elements contribute togene expression, cellular function, and disease. Functional characterization remains a challenge due to the abundance and complexity of candidate elements. Here, we develop a CRISPRi-based approach for multi-locus screening of putative transcription factor binding sites with a single truncated guide. A truncated guide with hundreds of sequence match sites can reliably disrupt enhancer activity, which expands the targeting scope of CRISPRi while maintaining repressive efficacy. We screen over 13,000 possible CTCF binding sites with 24 guides at 10nucleotides in spacer length. These truncated guides direct CRISPRi-mediated deposition of repressive H3K9me3 marks and disrupt transcription  factor binding at most sequence match target sites. This approach is valuable for elucidating functional transcription factor binding motifs or other repeated genomic sequences and is easily implementable with existing tools. Overall design: Jurkat or A375 cell lines treated with KRAB-dCas9 & guides targeting CTCF sites, CD81 promoter, or Safe Harbor control. Guides were 20nt in length or truncated (sg4 and sg8 and g[9nt])