EDITORIAL
Early studies of bacteriophages and their hosts revealed that some host strains were more resistant to certain phage isolates than were other closely related bacterial strains. Analysis of this phenomenon led to the discovery that many bacterial strains contain restriction/modification systems. Systems of this type include restriction endonucleases that cleave foreign DNA and modification enzymes that protect host DNA from cleavage. These restriction endonucleases provided the backbone for the development of DNA cloning technologies. Demonstration that bacterial hosts affected phage properties (1) and characterization of restriction and modification systems in Escherichia coli were provided in seminal papers by Luria and Human (1), Herbert Boyer (2), and Seymour Lederberg (3) in the Journal of Bacteriology (JB), as was demonstration that restriction occurs by DNA cleavage (4).
More recent studies have demonstrated that bacteria have other weapons in their arsenal to protect against foreign invaders. The initial observation of an unusual set of repeated sequences in the genomes of E. coli and other enteric bacteria was reported in JB by Nakata and coworkers (5, 6). This led to the discovery of CRISPR-Cas systems as immune systems that defend prokaryotes against foreign DNA and to subsequent work that characterized the sequence requirements for immunity (7). As was true of restriction endonucleases, the CRISPR-Cas defense mechanism has provided a set of novel tools that are now being exploited in a wide variety of genetic systems and have the potential to revolutionize genetic approaches in mammalian cells.
The views expressed in this Editorial do not necessarily reflect the views of the journal or of ASM.
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