A phage genome as it exists during a lysogenic infection.
Prophages are formed upon either upon chromosomal insertion or plasmid formation during infection and are lost either upon induction or curing.
The concept of prophage referred, historically, to an unknown, non-virion state that phages enter into upon lysogenization of a bacterium. Thus, in terms lysis generation, the prophage was a state that comes before the "phage" state, that is, defined for example as a virion. This is the definition from Adams (1959, InterScience, p. 441): "The form in which phages are perpetuated in lysogenic bacteria."
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