Publications by authors named "J G Modell"
Many CRISPR-Cas (clustered regularly interspaced short palindromic repeats and CRISPR-associated protein) systems, which provide bacteria with adaptive immunity against phages, are transcriptionally repressed in their native hosts. How CRISPR-Cas expression is induced as needed, for example, during a bacteriophage infection, remains poorly understood. In Streptococcus pyogenes, a non-canonical guide RNA tracr-L directs Cas9 to autorepress its own promoter.
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- CRISPR-Cas systems help bacteria defend against viruses called bacteriophages, but are often kept inactive to prevent self-harm.
- During phage infections, these systems can ramp up their defenses, and researchers found that phage-encoded proteins can enhance this response by lifting the auto-repression of Cas9.
- This newly discovered mechanism allows more bacterial cells to survive infections and reduces the chance of horizontal gene transfer, demonstrating that Cas9 acts as both a defender and a detector of phage threats.
Gene transfer agents (GTAs) are prophage-like entities found in many bacterial genomes that cannot propagate themselves and instead package approximately 5 to 15 kbp fragments of the host genome that can then be transferred to related recipient cells. Although suggested to facilitate horizontal gene transfer (HGT) in the wild, no clear physiological role for GTAs has been elucidated. Here, we demonstrate that the α-proteobacterium Caulobacter crescentus produces bona fide GTAs.
View Article and Find Full Text PDFProkaryotic organisms have developed multiple defense systems against phages; however, little is known about whether and how these interact with each other. Here, we studied the connection between two of the most prominent prokaryotic immune systems: restriction-modification and CRISPR. While both systems employ enzymes that cleave a specific DNA sequence of the invader, CRISPR nucleases are programmed with phage-derived spacer sequences, which are integrated into the CRISPR locus upon infection.
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- CRISPR-Cas systems help bacteria defend against viruses by using RNA guides to target and cut viral DNA.
- Bacteriophages, like λ, have their own recombination systems, specifically the Red system, which can help them evade CRISPR by mutating their target sequences.
- This Red system outperforms bacterial repair mechanisms, allowing phages to produce more variations that can resist CRISPR targeting, potentially aiding their spread among viruses.