Send to

Choose Destination
Anal Biochem. 1995 Apr 10;226(2):235-40.

A general method for detecting and sizing large plasmids.

Author information

Department of Microbiology and Molecular Genetics, School of Medicine, Loma Linda University, California 92350, USA.


We have devised a method for detecting and estimating the sizes of large bacterial plasmids in the presence of genomic DNA by pulsed-field gel electrophoresis (PFGE). Bacteria harboring plasmids were embedded in agarose and lysed using a rapid protocol. Plugs were incubated with S1 nuclease and subjected to PFGE in agarose gels. S1 nuclease converted supercoiled plasmids into full-length linear molecules. Large plasmids migrated as discrete bands that were readily observed after ethidium staining. Their sizes were reliably estimated by comparison with linear DNA markers. Without S1 digestion, supercoiled plasmids migrated at rates that were not a simple function of their molecular weights, making size determinations problematic. S1-PFGE detected megaplasmids up to 609 kilobases (kb) in six genera of bacteria (Agrobacterium, Escherichia, Klebsiella, Pseudomonas, Salmonella, and Staphylococcus). The procedure gave size values consistent with previous estimates for characterized megaplasmids. Eight new plasmids between 102 and 316 kb were discovered in Klebsiella and Staphylococcus. S1-PFGE avoids the difficulties of plasmid isolation, eliminates the preparation of probes, and does not require knowledge of restriction enzyme cleavage sites. It detects multiple large plasmids up to the limits of PFGE and can be used to screen for megaplasmids in many strains simultaneously.

[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Elsevier Science
Loading ...
Support Center