The synthesis of phage and host dna in the establishment of lysogeny

Abstract

A method of extraction is described which prevents excessive fragmentation of bacterial DNA. The larger bacterial DNA can then be separated from the phage DNA on sucrose gradients. The relative amounts of phage and host DNA made at various times during infection of Salmonella typhimurium with phage P22 leading to lysogeny have been determined. Phage-specific DNA synthesis begins at about 4 minutes, continues to increase for 2–4 minutes, and then decreases until complete repression is attained at 16 minutes. Autonomous phage DNA synthesis remains repressed from then on. Bacterial-specific synthesis proceeds at a decreasing rate until about 16 minutes, when almost complete inhibition is reached. When DNA synthesis recovers in the infected cells, only host-specific material is made. A new species of DNA, which is made only when phage DNA is synthesized, has been detected. The possible implications of these findings in the understanding of the lysogeny interaction is discussed.