The anatomy of the T5 bacteriophage DNA molecule

Abstract

The T5 bacteriophage DNA molecule, unlike the molecules from T2, P1, λ and T7 bacteriophage, contains interruptions at specific locations in both of its polynucleotide chains. When the molecule is denatured, it gives rise to polynucleotide chains which sediment in at least four different zones. By contrast, denatured T2, P1, λ and T7 DNA sediment as unimodal zones. The lengths of the polynucleotide chains -which comprise these zones were calculated through use of a relationship established for determining the relative lengths of polynucleotide chains from their rate of sedimentation in alkaline sucrose gradients. The positions of the interruptions along the molecule are under the genetic control of the phage and apparently are not a property of the host. The phenomenon is seen in another phage, PB, which is closely related to T5. The interruptions in the molecule are probably gaps in the polynucleotide chains. This conclusion was reached because the chains are not intact when the molecule is denatured in formamide, a mild organic denaturing agent. A number of models were proposed for ways in which the six polynucleotide chains could be arranged to form the intact duplex molecule. Two reannealing experiments were performed which confirmed some general features which all of the models had in common. The existence of gaps in the T5 DNA molecule helps to explain some earlier observations on the structure of the molecule and suggests interpretations for other results concerning its biological function.