How DnaK helps control early CRISPR defence in E. coli.

What is it about?

In this study, we investigated how E. coli starts building new CRISPR immune memory when it does not already have a matching defence. We found that the bacterial chaperone DnaK physically interacts with the Cas1–Cas2 complex, the proteins that add new DNA pieces into CRISPR sites, and holds this process back. In cells, DnaK limited CRISPR changes coming from the bacterium’s own chromosome, and this restraint was released when DnaK was removed or altered or when phage proteins were present. Biochemical experiments also showed that DnaK can reduce DNA binding and DNA integration by Cas1–Cas2, while live-cell imaging linked Cas1 behaviour to active DNA replication.

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Photo by National Institute of Allergy and Infectious Diseases on Unsplash

Photo by National Institute of Allergy and Infectious Diseases on Unsplash

Why is it important?

This matters because it suggests that DnaK may help protect the bacterial genome from harmful self-targeting during the earliest stage of CRISPR memory formation. Our findings also add a new layer to the CRISPR story by showing that a host-cell protein, not only CRISPR proteins themselves, could influence when and where new DNA is captured. More broadly, the study suggests a model in which Cas1–Cas2 is restrained until conditions associated with an invading genetic element help release it. Finally, we identified that Cas1-Cas2 complexes can act as biomarkers for DNA synthesis in cells.