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Most often in infectious disease, bacteria are the attackers.

But they, too, can be infected, by viruses and plasmids. And so in their genomes, bacteria have clustered regularly interspaced short palindromic repeats or CRISPRs u "a small RNA-based immune system," Rebecca Terns told BioWorld Today, "that protects prokaryotes and archaea from invaders."

The CRISPR system has two components. One consists of bacterial RNAs that binds to DNA or RNA from viral invaders. Once it is bound, it attracts a protein complex that silences those invaders.

There are multiple CRISPR systems, and Terns said that one interesting fact is that some …