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CRISPR transcript processing: a mechanism for generating a large number of small interfering RNAs.
Marko Djordjevic1, Magdalena Djordjevic, Konstantin Severinov
1Institute of Physiology and Biochemistry, Faculty of Biology, University of Belgrade, Belgrade, Serbia. dmarko@bio.bg.ac.rs
Biology Direct
|August 2, 2012
Summary
A minimal model explains CRISPR/Cas processing in E. coli, revealing strong linear amplification of crRNAs. This amplification depends on pre-crRNA degradation and can be modulated by CRISPR transcription and cas gene activity.
Area of Science:
- Microbiology
- Molecular Biology
- Systems Biology
Background:
- CRISPR/Cas is a prokaryotic defense system targeting foreign DNA.
- CRISPR transcripts (pre-crRNA) are processed into crRNAs by Cas proteins.
- Overexpression of cas genes in E. coli yields numerous crRNAs from few pre-crRNAs.
Purpose of the Study:
- To develop a minimal mathematical model of CRISPR/Cas processing.
- To explain experimental observations of crRNA generation in E. coli.
- To identify key factors influencing CRISPR/Cas system amplification.
Main Methods:
- Development of a minimal mathematical model.
- Parameterization using existing experimental data.
- Analysis of model dynamics under varying conditions.
Main Results:
- The model demonstrates strong linear amplification of crRNAs from minimal pre-crRNA decrease.
- Fast, non-specific pre-crRNA degradation by an unidentified nuclease is crucial for amplification.
- CRISPR transcription rate and cas gene overexpression levels influence crRNA production and saturation.
Conclusions:
- A model accurately explains CRISPR/Cas transcript processing and crRNA amplification in E. coli.
- Competition between specific processing and non-specific degradation dictates crRNA levels.
- Unidentified nucleases and transcriptional regulation are key control elements in the CRISPR response.
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