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dCas9 Fluorescence Loss Assays

The strength of dCas9 inhibition was measured in an Fluorescence Loss Assay. GFP, under the control of the lacUV5 promoter, is genomically inserted in an E. coli DH10ß strain. Three spacer were designed (Sp1 - 3) targeting either the -10 element of the lacUV5 promoter (Sp1) or the first 100 nucleotides of the GFP cds. A non-targeting Spacer (SpNT) was included as a control. All spacers were expressed via a single guide (sg)RNA expression cassette. Expression of dCas9 was IPTG inducible via the lacI/lac operator system.

Sp1 - 3 show clear reduction of GFP levels. Leakiness of lacI/lac operator system results in GFP expression even under un-induced conditions. The choice of spacers shows an effect on the efficiency of repression. Targeting the promoter region is more promising for repression of gene expression compared to targeting the beginning of the cds. For recommendations regarding spacer design see Larson et al., 2013.

Complete dCas9 expression cassette: https://parts.igem.org/Part:BBa_K3286008

sgRNA expression cassette (single target): https://parts.igem.org/Part:BBa_K3286003

dCas9 can further be used in a gene circuit under the control of an Anti-CRISPR. For more information see: https://parts.igem.org/Part:BBa_K3286010

Figure1: Fluorescence Loss Assay. Amount of GFP fluorescence under the induction of dCas9 targeting GFP.

The expression of dCas9 is regulated by an IPTG inducible expression system. Sp1 - 3 represent three different spacers targeting GFP or the associated promoter. SpNT represents a non-targeting spacer acting as a control.

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