Prophage

prophage [′prō‚fāj]

(virology)

Integrated unit formed by union of the provirus into the bacterial genome.

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Prophage 

a latent, or occult, noninfectious form of temperate bacteriophage that is present in lysogenic bacteria.

Prophage is the deoxyribonucleic acid (DNA) of a temperate bacteriophage combined with the DNA of a lysogenized bacterium. The DNA of a prophage is approximately 1/50 to 1/100 the size of the DNA of a bacterial chromosome and contains about 10⁵ pairs of nucleotides. Thus, a prophage is a complete genome of a phage and contains about 100 genes.

A prophage generally occupies a specific locus in a bacterial chromosome and is inherited like ordinary bacterial genes. The prophage of a λ-phage, for example, is localized in a chromosome of colibacillus together with the gene that controls the splitting of galactose. The location of a prophage is genetically controlled by its special region, which constitutes about 1/15 of the total length of the genome.

A prophage is nonpathogenic for a bacterial cell and is replicated over many generations simultaneously with the bacterial chromosome. However, in some growing lysogenic bacteria (approximately one cell per million), the prophage becomes infectious, that is, it becomes induced. As a result of induction, it is converted into an intracellular vegetative phage that is not bound to the bacterial chromosome. When this type of phage replicates, the bacterial cell undergoes lysis and dies. Individual lysogenic bacteria may carry several prophages.

A. V. KOLOBOV