F plasmids

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F plasmid derived replication origins

There are at least 3 kinds of replication origins that are derived from the F factor of Escherichia coli.


F plasmid derived origin used in most BACs

  • includes oriS, repE and the par genes
  • ~4.6 kb
  • used in pBeloBAC11 and other BACs
  • at copy number 4-6

"complete" F origin

  • includes repC, oriV, ccd operon, repD, oriS, repE and the par genes
  • ~9kb
  • used by Kris Prather in her F plasmids that she built when in Jay Keasling's lab [1]
  • at copy number 1-2


  • Episome: A circular piece of DNA that can replicate independently of the bacterial chromosome or integrate and replicate as part of the chromosome.
  • F factor: An episome in bacterial cells that confers the ability to act as a genetic donor during conjugation.
  • F+ cell: A bacterial cell possessing the fertility factor. Acts as a donor in conjugation.
  • F- cell: A bacterial cell that does not contain a fertility factor. Acts as a recipient in conjugation.
  • F' cell: A bacterial cell in which an integrated fertility factor spontaneously excises itself, taking part of the chromosome with it. The resulting episome therefore contains chromosomal material.
  • Hfr cell: A strain of bacteria exhibiting a high frequency of recombination, due to a chromosomally-integrated fertility factor. This strain is able to transfer all or part of the chromosome to recipient strains.

From [2].

Mating types

  • F+ mating with F- produces 2 F+
  • Hfr mating with F- produces Hfr and F-
  • F' mating with F- produces F' and F' merozygote

From [2].


  1. Jones KL and Keasling JD. Construction and characterization of F plasmid-based expression vectors. Biotechnol Bioeng. 1998 Sep 20;59(6):659-65. PubMed ID:10099385 | HubMed [Jones-BiotechnolBioeng-1998]
  2. [GeneticsGlossary]