CRISPR interference and priming varies with individual spacer sequences.

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• CRISPR-Cas systems provide adaptive immunity in bacteria against foreign DNA.
• Protospacer adjacent motif (PAM) and seed regions are critical for CRISPR interference and priming.
• The Escherichia coli Type I-E CRISPR-Cas system is a well-studied model for understanding these mechanisms.

Purpose of the Study:

• To reexamine the PAM and seed sequence requirements for interference and priming in E. coli Type I-E CRISPR-Cas.
• To investigate the influence of spacer sequences on these requirements.
• To identify novel functional PAM sequences and understand their role in adaptation.

Main Methods:

• Utilized multiple spacer sequences to test mutations in PAM and seed regions.
• Analyzed CRISPR interference and priming activities in response to these mutations.
• Investigated the acquisition of functional PAMs during naïve adaptation.

Main Results:

• CRISPR interference shows higher tolerance to PAM and seed mutations than previously known.
• Mutational tolerance and priming activity are significantly dependent on the specific spacer sequence.
• Identified numerous novel functional PAMs that support interference, priming, or both, contingent on the spacer.
• Functional PAMs are preferentially acquired during naïve adaptation, initiating rapid priming.

Conclusions:

• Spacer sequence plays a crucial role in modulating PAM and seed requirements for CRISPR-Cas function.
• Priming is a significant pathway for bacterial adaptation during initial infections.
• The findings expand our understanding of CRISPR-Cas specificity and adaptive immunity.