Prophage

Part of speech: noun

Definitions

1. A viral genetic component that integrates into the DNA of bacteria, remaining inactive until certain conditions trigger its expression
2. An element of viral DNA that merges with bacterial genes, capable of existing quietly until activated by environmental factors
3. A viral segment that becomes part of the bacterial genome, typically remaining dormant until specific stimuli prompt its activation

Etymology: Prophage is a deliberately built scientific term, and its building blocks are both Greek. The first part, "pro-", comes from the Ancient Greek preposition "pró", meaning "before" or "in front of". The second, "phage", comes from the Greek "phagein", "to eat", which gave English "phage" for a virus that devours bacteria, as in bacteriophage. Put together, the pieces suggest something that sits in front of the bacteriophage: the viral genome that has not yet begun its destructive work. The image behind the word is a kind of dormant stage. A virus of this type can slip its genetic material into a bacterium's own DNA, where it is copied along with the host's genes every time the cell divides. It stays quiet until some signal, such as stress on the cell, prompts it to activate, make copies of itself and break out. The name therefore describes the phage in its waiting position, before it has started killing.