ID   CSM6A_STRTR             Reviewed;         428 AA.
AC   A0A0A7HIX6;
DT   16-JAN-2019, integrated into UniProtKB/Swiss-Prot.
DT   04-MAR-2015, sequence version 1.
DT   25-MAY-2022, entry version 7.
DE   RecName: Full=CRISPR system endoribonuclease Csm6 {ECO:0000303|PubMed:25458845};
DE            EC=3.1.-.- {ECO:0000269|PubMed:28663439};
DE   AltName: Full=CRISPR type III-A associated protein Csm6-1 {ECO:0000305};
GN   Name=csm6 {ECO:0000303|PubMed:25458845};
OS   Streptococcus thermophilus.
OC   Bacteria; Firmicutes; Bacilli; Lactobacillales; Streptococcaceae;
OC   Streptococcus.
OX   NCBI_TaxID=1308;
RN   [1]
RP   NUCLEOTIDE SEQUENCE [GENOMIC DNA], FUNCTION IN PHAGE RESISTANCE, AND
RP   TARGETS SSRNA.
RC   STRAIN=DGCC8004;
RX   PubMed=25458845; DOI=10.1016/j.molcel.2014.09.027;
RA   Tamulaitis G., Kazlauskiene M., Manakova E., Venclovas C., Nwokeoji A.O.,
RA   Dickman M.J., Horvath P., Siksnys V.;
RT   "Programmable RNA shredding by the type III-A CRISPR-Cas system of
RT   Streptococcus thermophilus.";
RL   Mol. Cell 56:506-517(2014).
RN   [2]
RP   FUNCTION.
RC   STRAIN=DGCC8004;
RX   PubMed=27105119; DOI=10.1016/j.molcel.2016.03.024;
RA   Kazlauskiene M., Tamulaitis G., Kostiuk G., Venclovas C., Siksnys V.;
RT   "Spatiotemporal control of type III-A CRISPR-Cas immunity: coupling DNA
RT   degradation with the target RNA recognition.";
RL   Mol. Cell 62:295-306(2016).
RN   [3]
RP   FUNCTION, ACTIVITY REGULATION, SUBUNIT, AND MUTAGENESIS OF HIS-24;
RP   102-ASN--THR-107; THR-107; GLN-129 AND 371-ARG--HIS-376.
RC   STRAIN=DGCC8004;
RX   PubMed=28663439; DOI=10.1126/science.aao0100;
RA   Kazlauskiene M., Kostiuk G., Venclovas C., Tamulaitis G., Siksnys V.;
RT   "A cyclic oligonucleotide signaling pathway in type III CRISPR-Cas
RT   systems.";
RL   Science 357:605-609(2017).
CC   -!- FUNCTION: CRISPR (clustered regularly interspaced short palindromic
CC       repeat) is an adaptive immune system that provides protection against
CC       mobile genetic elements (viruses, transposable elements and conjugative
CC       plasmids). CRISPR clusters contain spacers, sequences complementary to
CC       antecedent mobile elements, and target invading nucleic acids. CRISPR
CC       clusters are transcribed and processed into CRISPR RNA (crRNA). The
CC       type III-A Csm complex binds crRNA and acts as a crRNA-guided RNase,
CC       DNase and cyclic oligoadenylate synthase; binding of target RNA cognate
CC       to the crRNA is required for all activities. In a heterologous host
CC       this Csm effector complex restricts ssRNA phage MS2, suggesting it may
CC       target RNA viruses in vivo. This protein is not part of the Csm
CC       complex. {ECO:0000269|PubMed:25458845}.
CC   -!- FUNCTION: Csm functions as a non-specific ssDNase. Base-pairing between
CC       crRNA and target RNA to form a ternary Csm complex activates a ssDNase
CC       activity; target RNA cleavage suppresses the ssDNase, a temporal
CC       control that prevents uncontrolled DNA degradation. Viral RNA
CC       transcripts probably tether the Csm complex to the viral genome,
CC       recruiting Cas10 ssDNA activity which is able to degrade DNA in the
CC       transcription bubble, spatially controlling the DNase activity.
CC       {ECO:0000269|PubMed:27105119}.
CC   -!- FUNCTION: A single-strand-specific endoribonuclease (ssRNase) that is
CC       approximately 1000-fold stimulated by cyclic oligoadenylate (cOA);
CC       although several species of cOA are synthesized by this organism only
CC       cyclic hexaadenylate (cA6) stimulates the ssRNase activity. Cleaves
CC       preferentially within GA or AA dinucleotides, although the presence of
CC       cA6 broadens the preference. Linear oligoadenylates do not activate the
CC       RNase. {ECO:0000269|PubMed:28663439}.
CC   -!- ACTIVITY REGULATION: Non-specific ssRNase activity is allosterically
CC       activated about 1000-fold by cyclic hexaadenylate (cA6), a second
CC       messenger produced by Cas10 of the ternary Csm effector complex in the
CC       presence of a cognate target RNA. ssRNase activity is inhibited by
CC       physiological concentrations of ATP (1 mM), activity is restored by
CC       cOA. {ECO:0000269|PubMed:28663439}.
CC   -!- SUBUNIT: Homodimer (PubMed:28663439). The composite ssRNase active site
CC       is formed at the dimer interface (By similarity).
CC       {ECO:0000250|UniProtKB:Q53W17, ECO:0000269|PubMed:28663439}.
CC   -!- DOMAIN: The N-terminal CRISPR-associated Rossman fold (CARF) probably
CC       binds the cA6 effector. ssRNase activity resides in the C-terminal HEPN
CC       domain. {ECO:0000250|UniProtKB:Q53W17}.
CC   -!- MISCELLANEOUS: Encoded in a type III-A CRISPR locus.
CC       {ECO:0000269|PubMed:25458845}.
CC   -!- SIMILARITY: Belongs to the CRISPR-associated Csm6 family.
CC       {ECO:0000305}.
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DR   EMBL; KM222358; AIZ03610.1; -; Genomic_DNA.
DR   AlphaFoldDB; A0A0A7HIX6; -.
DR   SMR; A0A0A7HIX6; -.
DR   GO; GO:0004519; F:endonuclease activity; IEA:UniProtKB-KW.
DR   GO; GO:0000166; F:nucleotide binding; IEA:UniProtKB-KW.
DR   GO; GO:0003723; F:RNA binding; IEA:UniProtKB-KW.
DR   GO; GO:0051607; P:defense response to virus; IEA:UniProtKB-KW.
DR   InterPro; IPR013489; CRISPR-assoc_prot_Csm6.
DR   Pfam; PF09659; Cas_Csm6; 1.
DR   TIGRFAMs; TIGR02672; cas_csm6; 1.
PE   1: Evidence at protein level;
KW   Antiviral defense; Endonuclease; Hydrolase; Nuclease; Nucleotide-binding;
KW   RNA-binding.
FT   CHAIN           1..428
FT                   /note="CRISPR system endoribonuclease Csm6"
FT                   /id="PRO_0000446126"
FT   REGION          1..145
FT                   /note="CARF domain"
FT                   /evidence="ECO:0000303|PubMed:28663439"
FT   REGION          146..428
FT                   /note="HEPN domain"
FT                   /evidence="ECO:0000303|PubMed:28663439"
FT   MUTAGEN         24
FT                   /note="H->A: About 100-fold reduction of single-stranded
FT                   ribonuclease (ssRNase) activity in presence of cyclic
FT                   oligoadenylates (cOA)."
FT                   /evidence="ECO:0000269|PubMed:28663439"
FT   MUTAGEN         102..107
FT                   /note="NLSSGT->ALSAGA: About 1000-fold reduction of ssRNase
FT                   activity in presence of cOA."
FT                   /evidence="ECO:0000269|PubMed:28663439"
FT   MUTAGEN         107
FT                   /note="T->A: About 100-fold reduction of ssRNase activity
FT                   in presence of cOA."
FT                   /evidence="ECO:0000269|PubMed:28663439"
FT   MUTAGEN         129
FT                   /note="Q->A: About 1000-fold reduction of ssRNase activity
FT                   in presence of cOA."
FT                   /evidence="ECO:0000269|PubMed:28663439"
FT   MUTAGEN         371..376
FT                   /note="RNKVAH->ANKVAA: No ssRNase activity even in presence
FT                   of cOA."
FT                   /evidence="ECO:0000269|PubMed:28663439"
SQ   SEQUENCE   428 AA;  49361 MW;  173D89817867FBFD CRC64;
     MKILISAVGT TDPISNNHDA ALLHIARNYR PDKIVLVYSQ EMMVKQDLIN KVLLSIEGYN
     PIIEIDSTIL NNDEVFLFDK MYEVMGQIVQ KYTNDDNEII LNLSSGTPQI ISALFALNRI
     NDYNTQAIQV ATPKNRANRE YTALTESEID ALIMENQDNR LDFVDRSIKD KSEKFTQALV
     KRHLRSLIAS FDYQAAEAII NRKEYNKLLS KKKIAYIREK LYDFSRVFKN QSILSDILSF
     PLDDSQKKAL NYYLMIDVLK EREHIADVLI KAKSLAEFVI EETIKKDHEG LIVFDGNLPK
     LNPSFPDCEA ILDDIDKKMK KSRGIEDTEE RIFSVQSTLN LLSYLNILEF YEYDSQLQTA
     INGILSLNGE RNKVAHGLSE IDTRLLSRKK LKQLSENLRL LLVDCLGIDS SYFNYYDKQN
     KELIKMLE