The Immune System's Compact Genomic Counterpart

Much of the human genome derives from self-serving DNA strands known as transposons. These genetic gypsies often jump to new chromosome locations, sometimes disabling genes and even triggering cancer. For that reason, a specialized group of RNA molecules known as piRNAs are the superheroes of animal genomes. piRNAs team up with certain proteins to shackle transposons in animal germline cells, creating a molecular defense that scientists liken to an immune system for the genome.
Science 4 January 2013: vol. 339 no. 6115 25-27