Protocol for robust gene knockout and reliable validation in human cell lines using quad-guide RNA vectors

CRISPR-Cas9 is a powerful tool for editing genomic loci, however achieving high knockout efficiency at certain targets remains challenging. Here, we present a protocol for gene knockout using an all-in-one, quad-guide RNA-expressing vector. We describe steps for plasmid construction, virus preparation, transduction, and subsequent gene editing and functional validation within DLD-1 colorectal adenocarcinoma cells. This strategy provides an efficient workflow for gene knockout that is rapidly confirmed through PCR amplification of mRNA derived from the targeted gene loci.