A viral SAVED protein with ring nuclease activity degrades the CRISPR second messenger cA4.

ABSTRACT: Type III CRISPR systems typically generate cyclic oligoadenylate second messengers such as cyclic tetra-adenylate (cA4) on detection of foreign RNA. These activate ancillary effector proteins which elicit a diverse range of immune responses. The Calp (CRISPR associated Lon protease) system elicits a transcriptional response to infection when CalpL (Calp Lon protease) binds cA4 in its SAVED (SMODS associated and fused to various effectors domain) sensor domain, resulting in filament formation and activation of the Lon protease domain, which cleaves the anti-Sigma factor CalpT, releasing the CalpS (Calp Sigma factor) for transcriptional remodelling. Here, we show that thermophilic viruses have appropriated the SAVED domain of CalpL as an anti-CRISPR, AcrIII-2 (second anti-CRISPR of type III

SUBMITTER: Orzechowski M 

PROVIDER: S-EPMC12751052 | biostudies-literature | 2025 Nov

REPOSITORIES: biostudies-literature