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The recently discovered prokaryotic CRISPR/Cas defence system provides immunity against viral infections and plasmid conjugation. It has been demonstrated that in Escherichia coli transcription of the Cascade genes (casABCDE) and to some extent the CRISPR array is repressed by heat-stable nucleoid-structuring (H-NS) protein, a global transcriptional repressor. Here we elaborate on the control of the E. coli CRISPR/Cas system, and study the effect on CRISPR-based anti-viral immunity. Transformation of wild-type E. coli K12 with CRISPR spacers that are complementary to phage Lambda does not lead to detectable protection against Lambda infection. However, when an H-NS mutant of E. coli K12 is transformed with the same anti-Lambda CRISPR, this does result in reduced sensitivity to phage infection. In addition, it is demonstrated that LeuO, a LysR-type transcription factor, binds to two sites flanking the casA promoter and the H-NS nucleation site, resulting in derepression of casABCDE12 transcription. Overexpression of LeuO in E. coli K12 containing an anti-Lambda CRISPR leads to an enhanced protection against phage infection. This study demonstrates that in E. coli H-NS and LeuO are antagonistic regulators of CRISPR-based immunity.

Original publication

DOI

10.1111/j.1365-2958.2010.07315.x

Type

Journal article

Journal

Mol Microbiol

Publication Date

09/2010

Volume

77

Pages

1380 - 1393

Keywords

Bacterial Proteins, Bacteriophage lambda, Base Sequence, Cloning, Molecular, DNA Footprinting, DNA, Bacterial, DNA, Intergenic, DNA-Binding Proteins, Escherichia coli K12, Escherichia coli Proteins, Gene Expression Regulation, Bacterial, Molecular Sequence Data, Mutation, Oligonucleotide Array Sequence Analysis, Promoter Regions, Genetic, Transcription Factors, Transcription, Genetic