Physical characterization of the DNA released from phage particles by heat inactivation

Abstract

A variety of phages including the T-phages [ 1, 2] P22 [3] and k [4] lose infectivity when exposed to ele- vated temperatures (50-60 °) particularly in low ionic strength medium or medium containing chelating agents. Heating also releases native DNA molecules from phage particles and for phages T7, SP-8, osaka 1 and a the DNA was shown to be released as unbroken molecules [4-6]. Since heat inactivation is a simple and rapid method it may offer advantages over those commonly used for extracting DNA from phage par- ticels. This paper reports studies undertaken to investi- gate the generality of heat inactivation as a method for extracting high molecular weight phage DNA and to extend the physical characterisation of heat released DNA molecules. The results show that for phages T1, T2, T3, T4, T7 and P22 heat inactivation of the particles was accompanied by the release of native DNA which in all cases consisted of unbroken mole- cules. Furthermore, the heat released DNA molecules from T2 and T7 had intact shlgle strands and a buoyant density identical to that of homologous DNA extracted with phenol.