Binding and interaction of acridine orange with intraphage DNA

Abstract

The interaction of acridine orange with intraphage DNA is weak, also perhaps the binding is little, although sufficient time is allowed in order that binding may reach equilibrium. The equilibrium dye-binding increases with the rise of temperature and becomes optimum at a temperature of 50–55° which is about 25–30° lower than the temperature of total DNA release and melting. Studies of interaction of acridine orange and ethidium bromide to intact phage indicate that, although the pahge DNA may be accessible for binding to both acridine orange and ethidium bromide, the binding is temperature specific for acridine molecules and perhaps involves at least two kinds of interaction. By contrast the interaction of ethidium bromide is by only one mode ( i.e. intercalation) and increases continuously with the rise of temperature. The phage DNA in situ has been found to be hyperchromic relative to native DNA in vitro to an extent (hyperchromicity 6 %) similar to that reported for T 2 phage and gives rise to considerable polarization of fluorescence when oriented. The temperature specific binding of acridine orange to phage DNA seems to arise as a result of some competition between bindings of weaker interaction and stronger interaction until an equilibrium between the two bindings is established. The latter may be controlled by the tight configuration and non-native conformation of the intraphage DNA. The interaction or binding is not likely to be determined by any selective permeability of the phage envelope.