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Type III-A CRISPR-associated protein Csm6 degrades cyclic hexa-adenylate activator using both CARF and HEPN domains

The type III CRISPR–Cas systems provide immunity against invading nucleic acids through the coordinated transcription-dependent DNA targeting and cyclic adenylate (cA(n))-activated RNA degradation. Here, we show that both these pathways contribute to the Streptococcus thermophilus (St) type III-A CR...

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Detalles Bibliográficos
Autores principales: Smalakyte, Dalia, Kazlauskiene, Migle, F. Havelund, Jesper, Rukšėnaitė, Audronė, Rimaite, Auguste, Tamulaitiene, Giedre, Færgeman, Nils J, Tamulaitis, Gintautas, Siksnys, Virginijus
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Oxford University Press 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7498309/
https://www.ncbi.nlm.nih.gov/pubmed/32766806
http://dx.doi.org/10.1093/nar/gkaa634
Descripción
Sumario:The type III CRISPR–Cas systems provide immunity against invading nucleic acids through the coordinated transcription-dependent DNA targeting and cyclic adenylate (cA(n))-activated RNA degradation. Here, we show that both these pathways contribute to the Streptococcus thermophilus (St) type III-A CRISPR–Cas immunity. HPLC-MS analysis revealed that in the heterologous Escherichia coli host the StCsm effector complex predominantly produces cA(5) and cA(6). cA(6) acts as a signaling molecule that binds to the CARF domain of StCsm6 to activate non-specific RNA degradation by the HEPN domain. By dissecting StCsm6 domains we demonstrate that both CARF and HEPN domains act as ring nucleases that degrade cA(n)s to switch signaling off. CARF ring nuclease converts cA(6) to linear A(6)>p and to the final A(3)>p product. HEPN domain, which typically degrades RNA, also shows ring nuclease activity and indiscriminately degrades cA(6) or other cA(n)s down to A>p. We propose that concerted action of both ring nucleases enables self-regulation of the RNase activity in the HEPN domain and eliminates all cA(n) secondary messengers in the cell when viral infection is combated by a coordinated action of Csm effector and the cA(6)-activated Csm6 ribonuclease.