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Physical and Functional Characteristics of R-Factor Deoxyribonucleic Acid Segregated into Escherichia coli Minicells¹

^a Laboratory of Biochemical Pharmacology, National Institute of Arthritis and Metabolic Diseases, Bethesda, Maryland 20014; Blood Research Laboratory, New England Medical Center Hospitals, Boston, Massachusetts 02111; and the Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111

ABSTRACT

Both fi⁺ and fi^– type R factors function as intact replicative units when segregated into Escherichia coli minicells. Hybridization studies demonstrate that at least 95% of the deoxyribonucleic acid (DNA) in R⁺ minicells is episomal in origin. About half of the DNA can be extracted in a closed circular form and about 75% of the DNA is membrane associated. DNA, ribonucleic acid, and protein synthesis proceeds in R⁺ minicells in contrast to R^– minicell controls. The system offers a unique opportunity to study a relatively small replicative unit in a native cell environment and a simple means of isolating large quantities of episomal DNA.

² Present address: Blood Research Laboratory, New England Medical Center Hospitals, Boston, Mass. 02111.

¹ Part of this work was presented at the Xth International Congress of Microbiology, Mexico City, Mexico, 9-15 August 1970.

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