Figure 6.

CRISPRi suppression of viral gene expression. CRISPRi can be used to target viral genomes, including multicopy EBV episomes. In this schematic, a sgRNA targets the dCas9–KRAB fusion to an EBV gene to downmodulate its expression. CRISPRi is advantageous when there are multiple copies of a host or viral gene, such as with EBV latently infected B cells which contain 5–50 viral genomes per cell. The targeted disruption with traditional CRISPR–Cas9 of high copy number genes, such as in EBV-infected cells or in areas of tumor cell genome amplification, is difficult because NHEJ repairs a subset correctly and because G2 arrest can also result (see text).