Cas1-Cas2 physically and functionally interacts with DnaK to modulate CRISPR Adaptation.

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Prokaryotic adaptive immunity relies on Cas1-Cas2 protein complexes to integrate mobile genetic elements (MGEs) DNA into CRISPR sites.
• The mechanisms governing de novo immunity, which lacks pre-existing interference complexes, are not fully understood.

Purpose of the Study:

• To elucidate the role of the chaperone DnaK in the process of naive adaptation and prokaryotic adaptive immunity.
• To investigate how DnaK influences the targeting of MGE DNA by the Cas1-Cas2 complex.

Main Methods:

• Utilizing Escherichia coli (E. coli) as a model system.
• Employing genetic manipulation (gene deletion and mutation) to study DnaK's function.
• Visualizing fluorescently labeled Cas1 in living cells using microscopy.

Main Results:

• DnaK was found to inhibit DNA binding and integration by the Cas1-Cas2 complex, thereby hindering naive adaptation.
• Inhibition of naive adaptation was reversed by DnaK deletion, mutation of its substrate-binding domain, or expression of a phage lambda protein.
• Cas1 foci formation in living cells was dependent on active DNA replication and significantly increased in DnaK-deficient cells.

Conclusions:

• DnaK acts as a restraint on naive adaptation, preventing the Cas1-Cas2 complex from targeting the host chromosome.
• DnaK's activity is crucial for maintaining a balance, allowing for MGE targeting only when necessary.
• A model is proposed where DnaK releases the Cas1-Cas2 complex to target MGE DNA upon specific triggers.