PMID:26586803

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

Each of the five known Pseudomonas aeruginosa anti-CRISPR proteins, including AcrF1, blocks spacer acquisition by the reconstituted type I-F CRISPR-Cas system

"Spacer acquisition was inhibited in the presence of each of the five different anti-CRISPR proteins tested (acrF1–5, Figure 4)."
A frame-shift allele of acrF1 loses the anti-acquisition activity as well as the anti-interference activity, which makes the annotation a mutant-phenotype inference

"A plasmid bearing a frame-shift mutation in the beginning of the acrF1 anti-CRISPR gene that inactivates its anti-interference function (40) also inactivated the anti-acquisition function."
The authors attribute the anti-acquisition effect to the same targets as the anti-interference effect, the Csy complex or Cas3

"We conclude that anti-CRISPR proteins that inhibit CRISPR interference in P. aeruginosa by targeting either the Csy complex or Cas3, also inhibit spacer acquisition."
The assay is a heterologous reconstitution of the Pseudomonas type I-F system in Escherichia coli, not an experiment in the natural host

"To determine if anti-CRISPR proteins also affect spacer acquisition we transformed E. coli (KD604) cells harboring pCas and pCsy plasmids with compatible plasmids expressing distinct anti-CRISPR proteins and monitored spacer acquisition (Figure 4)."

PMID:23242138

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

JBD30 gene 35, the gene of this entry, is the phage's anti-CRISPR gene and was the subject of the mutational test that the activity requires a translated protein

"We addressed this issue by performing experiments on JBD30 gene 35."
Gene 35 is required for JBD30 to replicate on a CRISPR-proficient host but not on a host lacking the CRISPR loci and cas genes

"a frameshift mutation was introduced into the phage JBD30 anti-CRISPR gene (gene 35). This mutant phage was unable to replicate on wild-type PA14 but still replicated robustly on the ΔCR/cas strain, demonstrating the requirement of the anti-CRISPR gene for replication"
Anti-CRISPR genes are necessary for phage infection of CRISPR-proficient hosts and sufficient to let a CRISPR-targeted phage evade immunity

"Mutation of the anti-CRISPR gene of a phage rendered it unable to infect bacteria with a functional CRISPR/Cas system"

PMID:26416740

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

Two of the three type I-F anti-CRISPR proteins characterised, one of them AcrF1, block the DNA-binding activity of the surveillance complex by binding different protein subunits, while the third acts on Cas3

"Two block the DNA-binding activity of the CRISPR-Cas complex, yet do this by interacting with different protein subunits, and using steric or non-steric modes of inhibition."

PMID:28340349

Structure Reveals Mechanisms of Viral Suppressors that Intercept a CRISPR RNA-Guided Surveillance Complex.

AcrF1 binds the Cas7f backbone of the Csy complex and prevents target binding

"AcrF1 binds to the Cas7f backbone and prevents target binding"
Two AcrF1 molecules bind one Csy complex, contacting four of its six Cas7f subunits

"The structure presented here explains how two AcrF1 proteins (i.e. AcrF1.1 and 1.2) bind to one Csy complex through interactions with four of the six Cas7f subunits"
The block is steric, with AcrF1 sitting on the Cas7f thumbs where the target strand must pass from one complementary guide segment to the next

"AcrF1 proteins sits on top of the Cas7.6f and Cas7.4f thumbs, blocking the transition of target DNA from 1 to 2 and segment 3 to 4, respectively."
The protein of this entry is 78 residues with a four-stranded antiparallel beta-sheet flanked by two alpha-helices

"AcrF1 is a small protein (78 residues) composed of a four-stranded antiparallel β-sheet, flanked on one side by two α-helices"
Whether the Cas7f web-domain shift is caused by AcrF1 could not be determined without a structure of the anti-CRISPR-free complex

"suggesting that AcrF1 binding may induce a conformational change that restricts access to the guide RNA (Figure 4E), though a structure of Csy complex without the anti-CRISPRs will be necessary to know that the AcrF1 protein is directly responsible for this observation"

file:9CAUD/JBD30_035/JBD30_035-uniprot.txt

UniProtKB record L7P7M1 (JBD30_035, Pseudomonas phage JBD30)

The entry is classified in the AcrIF1 family by CDD and Pfam signature matches

"DR CDD; cd22279; AcrIF1; 1."