The principal function of anti-CRISPR proteins is to interact with specific components of CRISPR-Cas systems, such as the effector nucleases, to avoid the destruction of the phage DNA (by binding or cleavage).
 
A phage introduces its DNA into a prokaryotic cell, usually the cell detects a sequence known as "target", that activates CRISPR-Cas immune system, but the presence of an initial sequence (before the target) encoding the formation of Acr proteins, avoids phage destruction.
Acr proteins are formed before the target sequence is read.
This way, the CRISPR-Cas system is blocked before it can develop a response.

The procedure starts with the CRISPR locus being transcribed into crRNAs (CRISPR RNA).
CrRNAs combine with Cas proteins forming a ribonucleoprotein complex called Cascade.
This complex surveys the cell to find complementary sequences of the crRNA.
When this sequence is found, the Cas3 nuclease is recruited to the Cascade, and the target DNA from the phage is cleaved.
But, for instance, when AcrF1 and AcrF2 are found (anti-CRISPR proteins), these interact with Cas7f and Cas8f-Cas5f, respectively, not allowing the binding to the phage DNA.
Moreover, the cleaving of the target is prevented by the union between AcrF3 and Cas3.

The majority of Acr genes are located next to anti-CRISPR-associated (Aca) genes, which encode proteins with a helix-turn-helix DNA-binding motif.
Aca genes are preserved, and researchers are using them to identify Acr genes, but the function of the proteins they encode is not totally clear.
The Acr-associated promoter produces high levels of Acr transcription just after the phage DNA injection into the bacteria takes place and, afterward, Aca proteins repress the transcription.
If this wasn't repressed, the constant transcription of the gene would be lethal to the phage.
Therefore, Aca activity is essential to ensure its survival.
The principal function of anti-CRISPR proteins is to interact with specific components of CRISPR-Cas systems, such as the effector nucleases, to avoid the destruction of the phage DNA (by binding or cleavage).  
A phage introduces its DNA into a prokaryotic cell, usually the cell detects a sequence known as "target", that activates CRISPR-Cas immune system, but the presence of an initial sequence (before the target) encoding the formation of Acr proteins, avoids phage destruction. Acr proteins are formed before the target sequence is read. This way, the CRISPR-Cas system is blocked before it can develop a response. 
The procedure starts with the CRISPR locus being transcribed into crRNAs (CRISPR RNA). CrRNAs combine with Cas proteins forming a ribonucleoprotein complex called Cascade. This complex surveys the cell to find complementary sequences of the crRNA. When this sequence is found, the Cas3 nuclease is recruited to the Cascade, and the target DNA from the phage is cleaved. But, for instance, when AcrF1 and AcrF2 are found (anti-CRISPR proteins), these interact with Cas7f and Cas8f-Cas5f, respectively, not allowing the binding to the phage DNA. Moreover, the cleaving of the target is prevented by the union between AcrF3 and Cas3. 
The majority of Acr genes are located next to anti-CRISPR-associated (Aca) genes, which encode proteins with a helix-turn-helix DNA-binding motif. Aca genes are preserved, and researchers are using them to identify Acr genes, but the function of the proteins they encode is not totally clear. The Acr-associated promoter produces high levels of Acr transcription just after the phage DNA injection into the bacteria takes place and, afterward, Aca proteins repress the transcription. If this wasn't repressed, the constant transcription of the gene would be lethal to the phage. Therefore, Aca activity is essential to ensure its survival.
Anti-CRISPR