Genetics of Bacteria and Viruses
A bacteriophage (or phage) is a bacterial virus, an obligatory parasite capable of either killing its bacterial host while producing numerous copies of itself (lytic growth) or establishing a mutually beneficial symbiosis with its host (lysogeny). Phages contain genomes that may be either RNA or DNA, in either single-stranded (ss) or double-stranded (ds) form, linear or circular. The nucleic acid is surrounded by a protein capsid, formed as a cylinder (in filamentous phage, such as coliphage M13) or a regular or elongated icosahedron; some phages (such as PRD1) contain a lipid layer inside or outside the protein shell. Some phage particles (virions) are made up from just an icosahedral capsid surrounding the genome (such as coliphage cI>X174), while others carry a tail attached to the capsid which may be short (as for coliphage T7), long and contractile (as for the coliphage T4), or long
Table 1 Some properties of commonly used coliphages.