Illustration of the DNA (deoxyribonucleic acid) translocation core complex from the T7 bacteriophage. Bacteriophages, or phages, are viruses that infect bacteria. They infect bacteria by injecting their DNA into the cell via a tail-like tube. T7 phages infect Escherichia coli. The T7 phage's tail apparatus does not extend all the way through E. coli's cell wall and so to infect the bacterial cell the T7 phage assembles a channel, known as the DNA translocation core complex, to extend its tail, allowing the DNA to be injected into the bacterial cytoplasm.