RT Journal Article
SR Electronic
T1 A target expression threshold dictates invader defense and autoimmunity by CRISPR-Cas13
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2021.11.23.469693
DO 10.1101/2021.11.23.469693
A1 Elena Vialetto
A1 Yanying Yu
A1 Scott P. Collins
A1 Katharina G. Wandera
A1 Lars Barquist
A1 Chase L. Beisel
YR 2021
UL http://biorxiv.org/content/early/2021/11/23/2021.11.23.469693.abstract
AB Immune systems must recognize and clear foreign invaders without eliciting autoimmunity. CRISPR-Cas immune systems in prokaryotes manage this task by following two criteria: extensive guide:target complementarity and a defined target-flanking motif. Here we report an additional requirement for RNA-targeting CRISPR-Cas13 systems: expression of the target transcript exceeding a threshold. This finding is based on targeting endogenous non-essential transcripts, which rarely elicited dormancy through collateral RNA degradation. Instead, eliciting dormancy required over-expressing targeted transcripts above a threshold. A genome-wide screen confirmed target expression levels as the principal determinant of cytotoxic autoimmunity and revealed that the threshold shifts with the guide:target pair. This expression threshold ensured defense against a lytic bacteriophage yet allowed tolerance of a targeted beneficial gene expressed from an invading plasmid. These findings establish target expression levels as a third criterion for immune activation by RNA-targeting CRISPR-Cas systems, buffering against autoimmunity and distinguishing pathogenic and benign invaders.HIGHLIGHTSCas13-induced dormancy requires RNA target levels to exceed an expression thresholdThe expression threshold can prevent cytotoxic self-targeting for endogenous transcriptsThe threshold shifts depending on the CRISPR RNA guide:target pairThe threshold allows cells to distinguish pathogenic and benign infectionsCompeting Interest StatementC.L.B. is a co-founder and member of the Scientific Advisory Board for Locus Biosciences as well as a member of the Scientific Advisory Board for Benson Hill. The other authors have no conflicts of interest to declare.