Traces of DNA prove the test of strength between viruses and bacteria

A nearly invisible battle rages on between Bacteria and Archaea on one side and viruses and other mobile elements on the other. This tug-of-war leaves its traces in the genomes of the involved parties and thus can be analyzed in respect of their co-evolution. One of the antiviral defense systems of Bacteria, the CRISPR system, contains pieces of viral DNA that provide direct insight into the history of previous viral attacks. Another indication of this battle is the disruption of transfer RNA genes used by viruses as attachment sites to facilitate their integration into the host genome.