Exploring CRISPR Interference by Transformation with Plasmid Mixtures: Identification of Target Interference Motifs...

Plasmid transformation into a bacterial host harboring a functional CRISPR-Cas system targeting a sequence in the transforming molecule can be specifically hindered by CRISPR-mediated interference. In this case, measurements of transformation efficacy will provide an estimation of CRISPR activity. However, in order to standardize data of conventional assays (using a single plasmid in the input DNA sample), transformation efficiencies have to be compared to those obtained for a reference molecule in independent experiments. Here we describe the use of a transforming mixture of plasmids that includes the non-targeted vector as an internal reference to obtain normalized data which are unbiased by empirical variations.