What is it about?
We investigated how the Cas1–Cas2 protein complex finds DNA to add new spacers to CRISPR sites in Escherichia coli. We used fluorescently tagged Cas1–Cas2 and DNA capture assays to follow functional complexes during normal growth, replication stress and DNA repair defects. We found that visible DNA-bound Cas1–Cas2 appeared only when the DNA-copying machinery was active, and accumulated at post-replicative DNA gaps, which are single-stranded or partly copied DNA regions left behind replication forks. Loss of RecFOR, which normally helps direct these gaps into repair, strongly increased DNA capture, while RecBCD was still required. This supports a model in which naïve CRISPR–Cas adaptation can use replication-dependent DNA repair intermediates as a source of new CRISPR spacers.
Featured Image
Photo by CDC on Unsplash
Why is it important?
This study helps explain how bacteria may begin building CRISPR immune memory when they do not yet have a spacer to guide them to an invader. The findings suggest that Cas1–Cas2 may be licensed by DNA structures that naturally arise during replication and repair, including during host-driven replication of mobile genetic elements. The work also clarifies how RecFOR and RecBCD shape naïve CRISPR adaptation, and suggests that Cas1–Cas2 foci could be useful readouts of replication-coupled DNA repair.
Perspectives
From our perspective, what stands out is the connection between seeing Cas1–Cas2 inside E. coli cells and measuring actual spacer acquisition at the CRISPR-1 locus. Foci disappeared when replisomes could not advance, intensified under replication stress, and became brighter when RecFOR-mediated gap repair was weakened, giving a coherent evidence chain. We were also struck that the work points to ordinary replication-repair intermediates, rather than a specialised CRISPR-only substrate, as a route into new immune memory. At the same time, the experimental assays use induced Cas1–Cas2 expression and chromosomal DNA gaps, so the model for mobile genetic elements remains grounded in, but not identical to, the E. coli system we tested.
Dr. Christian J Rudolph
Brunel University
Read the Original
This page is a summary of: Visualizing the interplay of Cas1–Cas2 with DNA replication-repair that creates CRISPR–Cas immunity, Nucleic Acids Research, June 2026, Oxford University Press (OUP),
DOI: 10.1093/nar/gkag564.
You can read the full text:
Contributors
The following have contributed to this page
