DNA replication of bacteriophage T5. 1. Fractionation of intracellular T5 DNA by agarose gel electrophoresis

Two forms of DNA may be isolated from gently lysed T5-infected bacteria. In neutral sucrose gradients a fast sedimenting form (fsf) is distinguishable from a slow sedimenting form (ssf) which moves at a rate similar to that of DNA extracted from mature T5 virus particles. A method of agarose gel electrophoresis is described which gives complete separation of the slow sedimenting from the fast sedimenting form. The DNA was extracted from the agarose using potassium iodide and isopycnic centrifugation; samples of the slow sedimenting form prepared by these methods were suitable for detailed structural studies.