Bacteriophage P1-mediated generalized transduction in Escherichia coli: Structure of abortively transduced DNA

Abstract

DNA was extracted from [ 3H]thymidine-labeled Escherichia coli infected with 32P-5-bromouracil-labeled transducing particles, and analyzed in equilibrium CsCl gradients. About 75% of the 32P-labeled transducing DNA equilibrated in the heavy region of the gradient. This nonchromosomally associated DNA, which represented abortively transduced DNA, remained fully heavy up to 5 hr after infection. Sedimentation of abortively transduced DNA in neutral and in alkaline sucrose gradients showed that both strands remained intact up to 3 hr after infection. When infected recipient bacteria were lysed by a nonionic detergent procedure, about 60% of the abortively transduced DNA could be recovered in a form which sedimented 1.7 to 1.8 times faster than linear P1 phage DNA in neutral sucrose gradients. Sedimentation of abortively transduced DNA and P1 prophage DNA in neutral sucrose gradients showed faster and slower sedimenting forms of abortively transduced DNA which corresponded to supercoiled and relaxed circular prophage DNA, respectively. Agarose gel electrophoresis of abortively transduced DNA showed bands which comigrated with circular prophage DNA. Treatment of abortively transduced DNA with sodium lauryl sulfate, with heat (70°), or with Pronase converted the DNA to a form which sedimented with linear P1 phage DNA in neutral sucrose gradients, and which migrated with linear P1 transducing particle DNA in agarose gels. The data suggest that abortively transduced DNA exists as a circular DNA-protein complex.