The Influence of Copy-Number of Targeted Extrachromosomal Genetic Elements on the Outcome of CRISPR-Cas Defense.

Konstantin Severinov,Ekaterina Semenova,Iaroslav Ispolatov

doi:10.3389/fmolb.2016.00045

Abstract

Prokaryotic type I CRISPR-Cas systems respond to the presence of mobile genetic elements such as plasmids and phages in two different ways. CRISPR interference efficiently destroys foreign DNA harboring protospacers fully matching CRISPR RNA spacers. In contrast, even a single mismatch between a spacer and a protospacer can render CRISPR interference ineffective but causes primed adaptation—efficient and specific acquisition of additional spacers from foreign DNA into the CRISPR array of the host. It has been proposed that the interference and primed adaptation pathways are mediated by structurally different complexes formed by the effector Cascade complex on matching and mismatched protospacers. Here, we present experimental evidence and present a simple mathematical model that shows that when plasmid copy number maintenance/phage genome replication is taken into account, the two apparently different outcomes of the CRISPR-Cas response can be accounted for by just one kind of effector complex on both targets. The results underscore the importance of consideration of targeted genome biology when considering consequences of CRISPR-Cas systems action.

Highlights

Reviewed by: Marko Djordjevic, University of Belgrade, Serbia Kurt Henry Piepenbrink, The University of Maryland School of Medicine, USA Peter Fineran, University of Otago, New Zealand
We present experimental evidence and present a simple mathematical model that shows that when plasmid copy number maintenance/phage genome replication is taken into account, the two apparently different outcomes of the CRISPR-Cas response can be accounted for by just one kind of effector complex on both targets
The Cas1 and Cas2 proteins from Escherichia coli, alone, are able to perform the spacer acquisition reaction in vitro (Nunez et al, 2015), and are sufficient in vivo in the absence of other Cas proteins to incorporate new spacers into a minimal CRISPR array consisting of a single repeat and short upstream leader sequence (Yosef et al, 2012; Arslan et al, 2014)

Summary

Introduction

Reviewed by: Marko Djordjevic, University of Belgrade, Serbia Kurt Henry Piepenbrink, The University of Maryland School of Medicine, USA Peter Fineran, University of Otago, New Zealand. In both models Cas3 binding to the effector complex at the fully matching protospacer with a functional PAM causes target destruction without adaptation.

Results

Conclusion