How the expression of Cas proteins in bacterial CRISPR-Cas immune system adapts to the constantly changing CRISPR structures and crRNA expression levels has been a long-standing unresolved scientific question. Prof. LI Ming and Prof. XIANG Hua’s lab at Institute of Microbiology of Chinese Academy of Sciences unraveled novel physiological functions of the guard RNA of CRISPR-Cas and provided a clue for this fundamental scientific question. This work was published in Cell Host & Microbe on September 1.
The research team first reported the guard RNA of CRISPR-Cas in 2021, which is a pair of CRISPR-Cas-regulated dual RNA toxin-antitoxin, named CreTA (CRISPR-regulated toxin-antitoxin). Researchers further discovered that the antitoxin crRNA-resembling antitoxin (CreA) not only guides Cas proteins to suppress the expression of the toxin gene creT, making the bacterial cells become "addicted" to Cas proteins (once Cas proteins are inactivated or inhibited, the toxin will be expressed and kill the bacterial cells), but also mediates the self-inhibitory regulatory circuit of Cas proteins, effectively avoiding the energy burden and self-immunity risk (targeting self-DNA) caused by excessive expression of Cas proteins.
Through extensive bioinformatics analysis, Cas-regulating RNA (CreR, lacking the coupling CreT toxin), similar molecules to CreA, are found to be widely present in Class 1 and Class 2 CRISPR systems (mainly type I and type V-A). More importantly, these CreR (or CreA) molecules can mediate the autoregulation of Cas proteins, not only sensing the concentration of intracellular crRNA and achieving their coordinated expression, but also effectively sensing the anti-CRISPR (Acr) proteins encoded by phages, thereby rapidly activating the high-level expression of Cas proteins in response to Acr attacks.
This discovery not only provides a new perspective on how CRISPR-Cas coordinates the expression of crRNA and Cas proteins, a fundamental scientific question in this field, but also reveals a new transcription-level anti-anti-CRISPR strategy.
This research was supported by the National Natural Science Foundation of China, the Strategic Priority Research Program of the Chinese Academy of Sciences, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, and the China Postdoctoral Science Foundation.
Contact:
LI Ming
Institute of Microbiology of Chinese
Phone: +86-10-64807064
E-mail: lim_im@im.ac.cn
Abstract: Researchers from Chinese Academy of Sciences uncovered that CRISPR-regulated toxin-antitoxins (CreTA), which safeguard the genetic integrity of CRISPR-Cas, also direct the negative autoregulation of Cas proteins. Importantly, such RNA-based Cas autoregulation not only reduces autoimmune risks of CRISPR-Cas, but also monitors crRNA abundance (to coordinate Cas and crRNA expression) and phage-encoded anti-CRISPR proteins (to trigger production of new Cas effectors).
Research