F plasmid

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The F-plasmid (abbreviation for fertility plasmid , also called fertility factor) is a plasmid that gives bacteria the ability to conjugate ( horizontal gene transfer ). The F plasmid enables directed gene transfer from the donor (this has the F factor, also known as F + ) to the recipient (F - ). The F plasmid itself is also very likely to be transferred to the recipient. As a result, the recipient (recipient) also becomes a donor (donor). Therefore, all bacterial cells that have an F plasmid are potential donor cells. After conjugation, both the donor and recipient will have an F plasmid.

Esther Lederberg and Luigi Luca Cavalli-Sforza discovered the F-factor and published the discovery together with the later Nobel Prize winner Joshua Lederberg .

Structural features

  • Origin of Transfer (OriT):
    DNA sequence at which conjugative transfer to the recipient begins. During the conjugation, the plasmid is transferred from the OriT to the recipient using the rolling circle replication. There the plasmid is cut open by an endonuclease (in some prokaryotes by relaxase ).
  • Origin of Replication (OriV):
    DNA sequence at which DNA replication begins. From the OriV, the F plasmid is propagated within the bacterium (one also speaks of vegetative propagation of the plasmid, although this term is somewhat misleading in this context). This increases the number of copies of the F plasmid (bacteria usually have several copies of the same plasmid).
  • tra region (transfer
    genes ): genes for the formation of the so-called F-pilus and a DNA transfer pore. The transfer genes are required to enable conjugation and rolling circle replication.
  • Insertion elements (IS):
    so-called selfish genes (DNA sequence segments that can integrate copies of their sequence elsewhere). Elements of similar sequence are also found on the bacterial chromosome. This enables the F plasmid to be integrated into the bacterial chromosome . An integrated F-plasmid behaves similarly to a non-integrated one and also enables conjugation. However, since the F plasmid has now also become part of the bacterial chromosome, DNA sequences or genes from the donor can now be transferred to the recipient, where recombination can occur. Bacterial strains with an integrated F plasmid are also called HfR strains ( high frequency of recombination ).

use

The discovery that the F plasmid can integrate into the bacterial chromosome opened up new possibilities for genetics. I.a. it enabled gene mapping by means of interrupted chromosome transfer . For the first time, it was also possible to move certain genes from one bacterium to another. Today there are special vectors for this , but they still use components of the F plasmid, e.g. B. two vector systems (one plasmid with OriT without tra region with selection markers and MCS for the gene to be cloned, the other much larger plasmid derived from F without OriT with tra genes).

A (similar) conjugative transfer is also possible between bacteria and z. B. yeast cells, or bacteria and plant cells possible (see. Agrobacterium tumefaciens ).

Another reason to take a closer look at the F-plasmid is that F-plasmids or other conjugatively transferable plasmids play a role in the rapid spread of antibiotic resistance (even between unrelated bacterial strains) (the F-plasmid has more than one OriV that are compatible with different bacterial strains or the OriV is also used by different bacterial strains). This means that a transposon with antibiotic resistance genes z. B. can "jump" (transpose) from the bacterial chromosome or another plasmid of strain A onto a conjugative plasmid , from there it can be conjugatively transferred to strain B. If the gene in strain B now brings an evolutionary advantage (e.g. under selection pressure from antibiotic use), the bacteria that received the plasmid will survive. As a result, so-called R plasmids with a large number of resistance genes can arise on one and the same plasmid, which can also be transmitted to pathogenic bacteria.

By acridine dyes , the F plasmid during cell division can be removed from a bacterial cell.

See also

literature

  • J. Lederberg, LL Cavalli, EM Lederberg: Sex compatibility in Escherichia coli. In: Genetics. 37 (6), Nov 1952, pp. 720-730.
  • Leland Hartwell, Leroy Hood; Michael L. Goldberg, Ann E. Reynolds, Lee M. Silver: Genetics: From Genes to Genomes. 4th edition. McGraw-Hill, New York, NY 2011, ISBN 978-0-07-352526-6 .
  • LJ Jerome, T. van Biesen, LS Frost: Degradation of FinP antisense RNA from F-like plasmids: the RNA-binding protein, FinO, protects FinP from ribonuclease E. In: J Mol Biol. 285 (4), 1999, p 1457-1473. doi: 10.1006 / jmbi.1998.2404 . PMID 9917389 .
  • DC Arthur, AF Ghetu, MJ Gubbins, RA Edwards, LS Frost, JN Glover: FinO is an RNA chaperone that facilitates sense-antisense RNA interactions. In: EMBO J. 22 (23), 2003, pp. 6346-6355. doi: 10.1093 / emboj / cdg607 . PMC 291848 (free full text). PMID 14633993 .

Individual evidence

  1. Lederberg, J., Cavalli, LL, and Lederberg, EM, Nov. 1952, "Sex compatibility in Escherichia coli", Genetics 37 (6): 720-730