F-plasmid
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TheF-plasmid(first namedFby one of its discoverersEsther Lederberg;also called thesex factorinE. coli,theF sex factor,or thefertility factor)[1][2][3]allows genes to be transferred from one bacterium carrying the factor to another bacterium lacking the factor byconjugation.The F factor was the firstplasmidto be discovered. Unlike other plasmids, F factor is constitutive for transfer proteins due to a mutation in the genefinO.[4]The F plasmid belongs toF-like plasmids,a class of conjugative plasmids that control sexual functions of bacteria with a fertility inhibition (Fin) system.[5]
Discovery
[edit]Esther M. LederbergandLuigi L. Cavalli-Sforzadiscovered "F,"[6]subsequently publishing withJoshua Lederberg.[7]Once her results were announced, two other labs joined the studies. "This was not a simultaneous independent discovery of F (I named this as Fertility Factor until it was understood.) We wrote to Hayes, Jacob, & Wollman who then proceeded with their studies."[8]The discovery of "F" has sometimes been confused withWilliam Hayes' discovery of "sex factor", though he never claimed priority. Indeed, "he [Hayes] thought F was really lambda, and when we convinced him [that it was not], he then began his work."[9]
Structure
[edit]The most common functional segments constituting F factors are:[10]
- OriT (Origin of Transfer): The sequence which marks the starting point of conjugative transfer.
- OriV (Origin of Vegetative Replication): The sequence starting with which the plasmid-DNA will be replicated in the recipient cell.
- tra-region (transfer genes): Genes coding the F-Pilus and DNA transfer process.
- IS (Insertion Elements) composed of one copy of IS2, two copies of IS3, and one copy of IS1000: so-called "selfish genes" (sequence fragments which can integrate copies of themselves at different locations).[11]
Some F plasmid genes and their Function:
- traA: F-pilin, Major subunit of the F-pilus.
- traN: recognizes cell-surface receptors[5]
Relation to the genome
[edit]Theepisomethat harbors the F factor can exist as an independentplasmidor integrate into the bacterial cell'sgenome.There are several names for the possible states:
- Hfr bacteriapossess the entire F episome integrated into the bacterial genome.
- F+bacteriapossess F factor as a plasmid independent of the bacterial genome. The F plasmid contains only F factor DNA and no DNA from the bacterial genome.
- F' (F-prime) bacteriaare formed by incorrect excision from the chromosome, resulting in F plasmid carrying bacterial sequences that are next to where the F episome has been inserted.
- F−bacteriado not contain F factor and act as the recipients.
Function
[edit]When an F+cell conjugates/mates with an F−cell, the result is two F+cells, both capable of transmitting the plasmid to other F−cells by conjugation. A pilus on the F+ cell interacts with the recipient cell allowing formation of a mating junction, the DNA is nicked on one strand, unwound and transferred to the recipient.[3][10]
The F-plasmid belongs to a class of conjugative plasmids that control sexual functions of bacteria with a fertility inhibition (Fin) system. In this system, a trans-acting factor, FinO, and antisense RNAs,FinP,combine to repress the expression of the activator geneTraJ.TraJ is atranscription factorthat upregulates thetraoperon.Thetraoperon includes genes required for conjugation and plasmid transfer. This means that an F+bacteria can always act as a donor cell. ThefinOgene of the original F plasmid (inE. coliK12) is interrupted by an IS3 insertion, resulting in constitutivetraoperon expression.[12][13]F+cells also have the surface exclusion proteins TraS and TraT on the bacterial surface. These proteins prevent secondary mating events involving plasmids belonging to the same incompatibility (Inc) group. Thus, each F+bacterium can host only a single plasmid type of any given incompatibility group.
In the case of Hfr transfer, the resulting transconjugates are rarely Hfr. The result of Hfr/F−conjugation is a F−strain with a new genotype. When F-prime plasmids are transferred to a recipient bacterial cell, they carry pieces of the donor's DNA that can become important inrecombination.Bioengineershave created F plasmids that can contain inserted foreign DNA; this is called abacterial artificial chromosome.
The first DNAhelicaseever described is encoded on the F-plasmid and is responsible for initiating plasmid transfer. It was originally calledE. coliDNA Helicase I,but is now known asF-plasmid TraI.In addition to being a helicase, the 1756 amino acid (one of the largest inE. coli) F-plasmid TraI protein is also responsible for both specific and non-specific single-stranded DNA binding as well as catalyzing the nicking of single-stranded DNA at the origin of transfer.
See also
[edit]References
[edit]- ^Dugger, Gordon (1976).A dictionary of life sciences.(London [usw.]): Macmillan). p. 130.ISBN978-0333194362.
- ^Hine, Robert (2008).A dictionary of biology(6th ed.). Oxford: Oxford University Press. p. 592.ISBN9780199204625.
- ^abLawley, TD; Klimke, WA; Gubbins, MJ; Frost, LS (15 July 2003)."F factor conjugation is a true type IV secretion system".FEMS Microbiology Letters.224(1): 1–15.doi:10.1016/S0378-1097(03)00430-0.PMID12855161.
- ^Yoshioka, Y; Ohtsubo, H; Ohtsubo, E (1987)."Repressor gene finO in plasmids R100 and F: constitutive transfer of plasmid F is caused by insertion of IS3 into F finO".Journal of Bacteriology.169(2): 619–623.doi:10.1128/jb.169.2.619-623.1987.ISSN0021-9193.PMC211823.PMID3027040.
- ^abFrankel, Gad; David, Sophia; Low, Wen Wen; Seddon, Chloe; Wong, Joshua L C; Beis, Konstantinos (18 August 2023)."Plasmids pick a bacterial partner before committing to conjugation".Nucleic Acids Research.doi:10.1093/nar/gkad678.PMC10516633.PMID37592747.
- ^As written by Esther Lederberg: "At this same time, L. Cavalli in Milan Italy, discovered the phenomenon of sterility from a different angle. Exchange of data showed that if I had done an experiment, he had planned to do it, but had completed another that we had planned. So we decided to pool forces and collaborate." Seehttp://www.estherMlederberg.com/Clark_MemorialVita/HISTORY52.html
- ^Lederberg, J., Cavalli, L. L., and Lederberg, E. M., Nov. 1952, "Sex compatibility in Escherichia coli", Genetics 37(6):720-730
- ^"Historical Notes About Fertility Factor F (version B)".www.esthermlederberg.com.Retrieved2023-07-14.
- ^"Historical Notes About Fertility Factor F (version A)".www.esthermlederberg.com.Retrieved2023-07-14.
- ^abArutyunov, Denis; Frost, Laura S. (2013-07-01). "F conjugation: Back to the beginning".Plasmid.70(1): 18–32.doi:10.1016/j.plasmid.2013.03.010.ISSN0147-619X.PMID23632276.
- ^Hartwell, Leland; Hood, Leroy; Goldberg, Michael L.; Reynolds, Ann E.; Silver, Lee M. (2011).Genetics:From Genes to Genomes; Fourth Edition.New York, NY: McGraw-Hill.ISBN978-0-07-352526-6.
- ^Jerome, LJ; van Biesen T; Frost LS (1999). "Degradation of FinP antisense RNA from F-like plasmids: the RNA-binding protein, FinO, protects FinP from ribonuclease E".J Mol Biol.285(4): 1457–1473.doi:10.1006/jmbi.1998.2404.PMID9917389.
- ^Arthur DC, Ghetu AF, Gubbins MJ, Edwards RA, Frost LS, Glover JN (2003)."FinO is an RNA chaperone that facilitates sense-antisense RNA interactions".EMBO J.22(23): 6346–55.doi:10.1093/emboj/cdg607.PMC291848.PMID14633993.