Unlike the deoxyribonucleic acid (DNA)-deficient minicells produced by Fparents, minicells produced by plasmid-containing strains contain significant amounts of plasmid DNA. We examined the ability of plasmid-containing minicells to synthesize ribonucleic acid (RNA) and protein. In vivo, minicells produced by Fparents are unable to incorporate radioactive precursors into acid-insoluble RNA or protein, whereas minicells produced by F', RI, or Col+ parents are capable of such synthesis. Using a variety of approaches, including polyacrylamide gel analysis of the RNA species produced and electron microscope autoradiography, we demonstrated that the synthesis observed in minicell preparations is a property of the plasmid-containing minicells and not a result of the few cells (approximately 1 per 106 minicells) contaminating the preparations. That the observed synthesis is of biological importance is suggested by the ability of plasmid-containing minicells to yield viable phage upon infection with T4.

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