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All organisms need to continuously adapt to changes in their environment. Through horizontal gene transfer, bacteria and archaea can rapidly acquire new traits that may contribute to their survival. However, because new DNA may also cause damage, removal of imported DNA and protection against selfish invading DNA elements are also important. Hence, there should be a delicate balance between DNA uptake and DNA degradation. Here, we describe prokaryotic antiviral defense systems, such as receptor masking or mutagenesis, blocking of phage DNA injection, restriction/modification, and abortive infection. The main focus of this review is on CRISPR (clustered regularly interspaced short palindromic repeats)/Cas (CRISPR-associated), a prokaryotic adaptive immune system. Since its recent discovery, our biochemical understanding of this defense system has made a major leap forward. Three highly diverse CRISPR/Cas types exist that display major structural and functional differences in their mode of generating resistance against invading nucleic acids. Because several excellent recent reviews cover all CRISPR subtypes, we mainly focus on a detailed description of the type I-E CRISPR/Cas system of the model bacterium Escherichia coli K12.

Original publication

DOI

10.1146/annurev-genet-110711-155447

Type

Journal article

Journal

Annu Rev Genet

Publication Date

2012

Volume

46

Pages

311 - 339

Keywords

Amino Acid Motifs, Bacteriophages, CRISPR-Associated Proteins, DNA Helicases, DNA, Viral, Deoxyribonucleases, Type I Site-Specific, Endodeoxyribonucleases, Escherichia coli K12, Escherichia coli Proteins, Gene Expression Regulation, Bacterial, Genes, Bacterial, Lysogeny, Prophages, Species Specificity, Virus Internalization