A Salmonella phage-P22 mutant defective in abortive transduction

In the course of a lytic infection the Salmonella phage P22 occasionally encapsulates bacterial DNA instead of phage DNA. Thus, phage lysates include two classes of viral particles. Phage particles carrying bacterial DNA are referred to as transducing particles and deliver this DNA to a host as efficiently as particles carrying phase DNA. Once injected, the transduced DNA can either recombine with the recipient chromosome to form a "complete" transductant, or it can establish itself as an expressible, nonreplicating genetic element and form an "abortive" transductant. In this work, we describe a P22-phage mutant with reduced ability to form abortive transductants. The mutation responsible for this phenotype, called tdx-1, was found as one of two mutations contributing to the high-transducing pheno-type of the P22-mutant HT12/4. In addition, the tdx-1 mutation is lethal when combined with an erf am mutation. The tdx-1 mutation has been mapped to a region of the P22 genome that encodes several injected proteins and may involve more than one mutant locus. The phenotypes of the tdx-l mutation suggest that the Tdx protein(s) normally assist in the circularization of the P22 genome and also contribute to the formation of DNA circles thought to be required for abortive transduction.