PMID:21398535

Non-identity-mediated CRISPR-bacteriophage interaction mediated via the Csy and Cas3 proteins.

Csy3 and Csy1 are not strictly required for crRNA accumulation, unlike Csy2 and Csy4

"proteins Csy4 and Csy2 are essential for small CRISPR RNA (crRNA) production in vivo, while the Csy1 and Csy3 proteins are not absolutely required for production of these small RNAs"
The PA14 Yersinia-subtype locus was reported not to confer resistance to phage DMS3, acting instead on biofilm formation

"the Yersinia-subtype CRISPR region of Pseudomonas aeruginosa strain UCBPP-PA14 plays no detectable role in viral immunity but instead is required for bacteriophage DMS3-dependent inhibition of biofilm formation"

PMID:21536913

RNA-guided complex from a bacterial immune system enhances target recognition through seed sequence interactions.

Csy1-4 assemble into a 350 kDa crRNA-containing surveillance complex that promotes guide-target hybridization

"the Csy proteins (Csy1-4) assemble into a 350 kDa ribonucleoprotein complex that facilitates target recognition by enhancing sequence-specific hybridization between the CRISPR RNA and complementary target sequences"
Target recognition initiates at a seed sequence at the crRNA spacer 5' end

"Target recognition is enthalpically driven and localized to a "seed sequence" at the 5' end of the CRISPR RNA spacer"

PMID:23242138

Bacteriophage genes that inactivate the CRISPR/Cas bacterial immune system.

The PA14 type I-F locus restricts replication of CRISPR-sensitive phages

"The CRISPR-sensitive phages fail to replicate on PA14 due to the action of the CRISPR/Cas system14, but are able to replicate on PA14"

PMID:26416740

Multiple mechanisms for CRISPR-Cas inhibition by anti-CRISPR proteins.

Anti-CRISPR proteins block the DNA-binding activity of the assembled type I-F complex by contacting different subunits

"Two block the DNA-binding activity of the CRISPR-Cas complex, yet do this by interacting with different protein subunits"

PMID:26586803

Foreign DNA acquisition by the I-F CRISPR-Cas system requires all components of the interference machinery.

A clean csy3 deletion abolishes new spacer acquisition

"Deleting the csy3 gene (lane 6), or mutating the catalytic residue His29 of Csy4 nuclease (lane 7) that is needed for generation of mature crRNA also abolished spacer acquisition"
Both naive and primed adaptation by the type I-F system require the intact Csy complex and crRNA

"both modes require, in addition to Cas1 and Cas2, intact Csy complex, an ortholog of the E. coli Cascade, and crRNA"

PMID:28985564

Cryo-EM Structures Reveal Mechanism and Inhibition of DNA Targeting by a CRISPR-Cas Surveillance Complex.

The structural work is on the Pseudomonas aeruginosa type I-F Csy complex

"The structural studies we describe here are focused on the type I-F Csy (CRISPR system yersinia) found in Pseudomonas aeruginosa"
Six interlocking Cas7f copies lie along the crRNA spacer

"Cas6f is located at the 3′ stem-loop of the crRNA, Cas8f and Cas5f are located at the 5′ handle of crRNA, and six interlocking copies of Cas7f are located along the length of the crRNA spacer"
A Cas7f beta-hairpin threads through each kink and pins the crRNA-DNA heteroduplex to the backbone

"hairpin emanating from the adjacent Cas7f subunit threads through each of these gaps spaced along the backbone, effectively pinning the RNA:DNA heteroduplex to the Csy complex backbone"
One Cas7f residue lines the PAM-proximal DNA-binding pocket, which is dominated by Cas8f

"Numerous positively charged residues line this DNA binding pocket, including residues from Cas7.6f (K299), the Cas5f thumb (R90), and especially the Cas8f hook (R24, K28, K31, R59, K71 and R78)"

PMID:32170016

Inhibition mechanisms of AcrF9, AcrF8, and AcrF6 against type I-F CRISPR-Cas complex revealed by cryo-EM.

Composition and stoichiometry of the type I-F Csy surveillance complex

"The Csy complex is comprised of four types of Cas proteins (Cas5f-8f) and a single 60-nt crRNA"
Six Cas7f copies form the spiral backbone between the Cas6f head and the Cas5f-Cas8f tail

"the maps exhibit an asymmetric spiral, with one Cas6f subunit in the head, one Cas5f and one Cas8f in the tail, and six Cas7f comprising the spiral backbone"
Cas7f contacts the crRNA sugar-phosphate backbone through an arginine-rich surface

"Cas7f and crRNA form multiple hydrogen bonds, which mostly occur between the arginine-rich region (F32, R34, R68, Q95, R168, Q247, Q276, K277, R283, S308, R350) and the sugar-phosphate backbone of crRNA"
crRNA recognition by Cas7f is sequence-independent

"This finding indicates the nonsequence-specific crRNA recognition mode of Cas7f"
Cas7f thumbs kink the crRNA at six-nucleotide intervals

"The thumbs of the spiral backbone proteins (Cas7f) distort the crRNA at 6-nt intervals"
A lysine-rich Cas7f patch is critical for DNA binding by the complex and is the surface anti-CRISPR proteins compete for

"a lysine-rich region of the Cas7f subunit (K76, K78, K84, and K256) has been reported to be critical for DNA binding by the Csy complex"