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A team of researchers has unlocked the key to how bacteria are able to “steal” genetic information from viruses and other foreign invaders for use in their own immunological memory system. The team has shown that bacteria need only two proteins to facilitate this process, Cas1 and Cas2.
Bacteria face a never-ending onslaught from viruses and invading strands of nucleic acid known as plasmids. To survive this onslaught, bacteria and archaea deploy a variety of defense mechanisms, including an adaptive-type immune system that revolves around a unit of DNA known as CRISPR, which stands for Clustered Regularly Interspaced Short Palindromic Repeats. A CRISPR unit of DNA is made up of “repeat” elements, base-pair sequences ranging from 30 to 60 nucleotides in length, separated by “spacer” elements, variable sequences that are also from 30 to 60 nucleotides in length. The memorizing proteins – Cas1 and Cas2 – recognize repeating sequences in CRISPR loci and target these sites for the spacer insertion process. These findings could provide an alternative way of introducing needed genetic information into a human cell or correcting a problem in an existing genome.Image credit: Megan Riel-Mehan for UC Berkeley
