9nq7

Structural highlights

Function

CSM5_STRTR CRISPR (clustered regularly interspaced short palindromic repeat) is an adaptive immune system that provides protection against mobile genetic elements (viruses, transposable elements and conjugative plasmids). CRISPR clusters contain spacers, sequences complementary to antecedent mobile elements, and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA). The type III-A Csm effector complex binds crRNA and acts as a crRNA-guided RNase, DNase and cyclic oligoadenylate synthase; binding of target RNA cognate to the crRNA is required for all activities. In a heterologous host this Csm effector complex restricts ssRNA phage MS2, suggesting it may target RNA viruses in vivo.^[1] Csm functions as a non-specific ssDNase. Base-pairing between crRNA and target RNA to form a ternary Csm complex activates a ssDNase activity; target RNA cleavage suppresses the ssDNase, a temporal control that prevents uncontrolled DNA degradation. Viral RNA transcripts probably tether the Csm complex to the viral genome, recruiting Cas10 ssDNA activity which is able to degrade DNA in the transcription bubble, spatially controlling the DNase activity.^[2] This subunit might be involved in maturation of a crRNA intermediate to its mature form.^[3]

References

1. ↑ Tamulaitis G, Kazlauskiene M, Manakova E, Venclovas C, Nwokeoji AO, Dickman MJ, Horvath P, Siksnys V. Programmable RNA shredding by the type III-A CRISPR-Cas system of Streptococcus thermophilus. Mol Cell. 2014 Nov 20;56(4):506-17. doi: 10.1016/j.molcel.2014.09.027. Epub 2014 , Nov 6. PMID:25458845 doi:http://dx.doi.org/10.1016/j.molcel.2014.09.027
2. ↑ Kazlauskiene M, Tamulaitis G, Kostiuk G, Venclovas C, Siksnys V. Spatiotemporal Control of Type III-A CRISPR-Cas Immunity: Coupling DNA Degradation with the Target RNA Recognition. Mol Cell. 2016 Apr 21;62(2):295-306. doi: 10.1016/j.molcel.2016.03.024. PMID:27105119 doi:http://dx.doi.org/10.1016/j.molcel.2016.03.024
3. ↑ Tamulaitis G, Kazlauskiene M, Manakova E, Venclovas C, Nwokeoji AO, Dickman MJ, Horvath P, Siksnys V. Programmable RNA shredding by the type III-A CRISPR-Cas system of Streptococcus thermophilus. Mol Cell. 2014 Nov 20;56(4):506-17. doi: 10.1016/j.molcel.2014.09.027. Epub 2014 , Nov 6. PMID:25458845 doi:http://dx.doi.org/10.1016/j.molcel.2014.09.027