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Covalently closed circular DNA molecules deficient in superhelical density as intermediates in plasmid life cycle

Nature volume 261, pages 516–519 (1976)Cite this article

Abstract

WE have described1 the replication of the conjugative R plasmid, RSF1040, a deletion mutant of R6K (ref. 2). RSF1040 possesses two distinct origins and replication generally proceeds from one or the other in an asymmetrically bidirectional mode to a unique terminus1, although in several instances molecules with two simultaneous initiations were observed2. During the course of examining the kinetic behaviour of replicating RSF1040 DNA (ref. 1), we observed 3H-thymidine pulse-labelled material that had a greater buoyant density in CsCl–ethidium bromide gradients than did mature covalently closed circular (form I) plasmid DNA. The nature of this material (‘heavy DNA’) and its relationship to the replication cycle are the subjects of this report.

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Authors and Affiliations

  1. Department of Microbiology, School of Medicine, University of Washington, Seattle, Washington, 98195

    JORGE H. CROSA, LINDA K. LUTTROPP & STANLEY FALKOW

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  1. JORGE H. CROSA
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  2. LINDA K. LUTTROPP
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  3. STANLEY FALKOW
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CROSA, J., LUTTROPP, L. & FALKOW, S. Covalently closed circular DNA molecules deficient in superhelical density as intermediates in plasmid life cycle. Nature 261, 516–519 (1976). https://doi.org/10.1038/261516a0

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