Abstract
<jats:p>Programmable transcription activators are central to functional genomics, gene therapy, and synthetic biology. However, application of the most versatile CRISPR activators (CRISPRa) is hampered by the bulky size and compact CRISPR systems are constrained by the requirement of long protospacer adjacent motifs (PAMs). To address these limitations, we repurposed the TIGR-Tas RNA-guided DNA-targeting system as a versatile platform for gene activation. By systematically optimizing the fusion architecture of a nuclease-inactivated TasR with gene activation domains, we achieved robust, specific, and multiplexable transcriptional activation of endogenous human genes. This TIGR activation (TIGRa) system could be a superior alternative to CRISPRa systems due to its extreme compactness and potentially PAM-independent targeting capability.</jats:p>