CRISPR activation (CRISPRa) is a type of CRISPR tool that uses modified versions of CRISPR effectors without endonuclease activity, with added transcriptional activators on dCas9 or the guide RNAs (gRNAs). Like for CRISPR interference, the CRISPR effector is guided to the target by a complementary guide RNA. However, CRISPR activation systems are fused to transcriptional activators to increase expression of genes of interest. Such systems are usable for many purposes including but not limited to, genetic screens and overexpression of proteins of interest.The most commonly-used effector is based on Cas9 (from Type II systems), but other effectors like Cas12a (Type V) have been used as well.