| Abstract: | Naturally occurring defective phage particles, which do not form plaques on any known host, but have a restricted host killing range, appear to be widely distributed. The defective phages are produced spontaneously but can be induced, at much higher levels, by chemical and physical agents which interfere with metabolism or structure of DNA. The defective phages discussed in this article have been divided into various categories on the basis of their structural complexity, which ranges from what appears to be phage tail components through to intact phage particles, and the source of the DNA packaged into the heads of the phage-like particles. The evolution of the defective phages is discussed and the possibility is entertained that they may have originated from temperate phages. |
