MOLECULAR STRUCTURE OF TRANSDUCING PARTICLES OF SALMONELLA-PHAGE P22 .I. DENSITY GRADIENT ANALYSIS OF INTACT PHAGES

The origin of DNA in transducing particles of Salmonella-phage P22 was investigated. DNA formed before or after phage infection of cells was differentially density-labeled with 5-bromodeoxyuridine. The buoyant densities of intact phages were analyzed in CsCl-density-gradients. The following results were obtained: 1. Plaque-forming and his+-transducing particles of both the wildtype-phage P22H1 and the clear-plaque mutant P22H5 have the same density. 2. 90% of DNA in transducing particles is normally formed before infection of the cells and 10% after infection. 3. A second group of transducing particles contains only about 20% of original bacterial DNA formed before infection. 80% of the DNA is synthesized after infection of the bacteria. 4. The origin of after-infection-DNA in transducing particles and its genetic information, if any, is unknown. 5. The results with wildtype-phage P22H1 and non-lysogenizing mutant P22H5 are identical. © 1968 Springer-Verlag.