Bacterial cGAS: Triggering Immunity with Viral RNA

Bacterial cyclic GMP-AMP synthase (cGAS) in the CBASS system senses viral RNA to initiate immunity in bacteria. Researchers investigated the activation mechanism of type I CBASS cyclases in staphylococci and found that a viral RNA, called cabRNA, activates the cyclase Ssc-CdnE03. The cabRNA contains secondary structures that are essential for cyclase activation. Mutations in positively charged residues of the cyclase disrupt the binding of cabRNA and impair cGAMP production. The study also revealed that other cyclases, such as Sha-CdnE01, from different CBASS systems can also be activated by cabRNA.