The CRISPR/Cas bacterial immune system cleaves bacteriophage and plasmid DNA

Abstract

Bacteria and Archaea have developed several defence strategies against foreign nucleic acids such as viral genomes and plasmids. Among them, clustered regularly interspaced short palindromic repeats (CRISPR) loci together with cas (CRISPR-associated) genes form the CRISPR/Cas immune system, which involves partially palindromic repeats separated by short stretches of DNA called spacers, acquired from extrachromosomal elements. It was recently demonstrated that these variable loci can incorporate spacers from infecting bacteriophages and then provide immunity against subsequent bacteriophage infections in a sequence-specific manner. Here we show that the Streptococcus thermophilus CRISPR1/Cas system can also naturally acquire spacers from a self-replicating plasmid containing an antibiotic-resistance gene, leading to plasmid loss. Acquired spacers that match antibiotic-resistance genes provide a novel means to naturally select bacteria that cannot uptake and disseminate such genes. We also provide in vivo evidence that the CRISPR1/Cas system specifically cleaves plasmid and bacteriophage double-stranded DNA within the proto-spacer, at specific sites. Our data show that the CRISPR/Cas immune system is remarkably adapted to cleave invading DNA rapidly and has the potential for exploitation to generate safer microbial strains.

Strong bias in the bacterial CRISPR elements that confer immunity to phage

“…Recent research, first described in 2002, has demonstrated the importance of a novel adaptive mechanism that provides bacteria immunity to phage 7,8 , that is based on clustered regularly interspaced short palindromic repeats (CRISPR) loci and their associated genes (cas) [9][10][11] . CRISPR-Cas immunity involves a multistep process that begins with the acquisition of short, exogenous nucleic acid fragments called spacers.…”

Diversity, evolution, and therapeutic applications of small RNAs in prokaryotic and eukaryotic immune systems

“…Although it was proposed that the PAM motif recognized by the CRISPR-Cas system, which was initially used to recognize protospacers for spacer insertion, is the marker which the complex uses to identify foreign DNA, it has been shown in E. coli that only 6 of the 7 nucleotides of the PAM need to be matched to the crRNA for the effector complex to cleave the DNA [117]. The complex might rely on Csn1 (Cas5) in order to cleave the foreign DNA after it is recognized [51].…”

Generation of the Adenovirus Vector-Mediated CRISPR/Cpf1 System and the Application for Primary Human Hepatocytes Prepared from Humanized Mice with Chimeric Liver

“…[1][2][3] Therefore, its potential is being explored in the research for treatment of human diseases such as sickle cell anemia, 4) hemophilia, 5,6) and human immunodeficiency virus (HIV) infection. 7) Liver diseases have been also regarded as targets of genome editing applications because of the variety of serious inherited and acquired genetic disorders caused by mutations in single genes.…”