Elucidating the mechanisms which lead to the development of a living organism is one of the most fascinating topic of modern biology. Processes as diverse as the embryonic development of higher eukaryotes, the mating cycle of lower eukaryotes, the division cycle of prokaryotes or the parasitic life cycle of viruses all depend on the accurate expression of the genetic information stored in the genome of the respective organisms. Entire regulatory cascades are required to express the proper functions at the correct time and appropriate level in order to produce structures of the complexity of an infective phage particle, an insect wing or a mammalian limb.
Bacteriophages prove to be useful organisms in addressing such questions about regulatory processes.
They are easy to propagate, have a short 'generation time' and mutations affecting any phage function are readily available. Many of the molecular mechanisms underlying single regulatory steps are understood or are studied intensively. Insights gained from these prokaryotic systems turned out to be valuable stimuli for investigations on analogous mechanisms in the more complex higher organisms. Even though the general scheme of the parasitic life cycle is common to most bacteriophages, different classes of phages show clearly distinct ways to regulate the expression of their genetic information. The investigation of phages different from T4 or l thus harbours the potential to extend and deepen our knowledge about the diversity of regulatory mechanisms found in nature.