bacteriophages

(= phages)

Viruses that infect bacteria. The bacteriophages that attack Escherichia coli are termed coliphages, examples of these are lambda phage and the T-even phages, T2, T4 and T6. Basically, phages consist of a protein coat or capsid enclosing the genetic material, DNA or RNA, that is injected into the bacterium upon infection. In the case of virulent phages all synthesis of host DNA, RNA and proteins ceases and the phage genome is used to direct the synthesis of phage nucleic acids and proteins using the host\'s transcriptional and translational apparatus. These phage components then self-assemble to form new phage particles. The synthesis of a phage lysozyme leads to rupture of the bacterial cell wall releasing, typically 100-200 phage progeny. The temperate phages, such as lambda, may also show this lytic cycle when they infect a cell, but more frequently they induce lysogeny. The study of bacteriophages has been important for our understanding of gene structure and regulation. Lambda has been extensively used as a vector in recombinant DNA studies.