F-plasmid
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The F-plasmid (first named F by one of its discoverers
Discovery
Esther M. Lederberg and Luigi L. Cavalli-Sforza discovered "F," [6] subsequently publishing with Joshua 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 with William 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
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
The episome that harbors the F factor can exist as an independent plasmid or integrate into the bacterial cell's genome. There are several names for the possible states:
- Hfr bacteria possess the entire F episome integrated into the bacterial genome.
- F+ bacteria possess 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) bacteria are 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− bacteria do not contain F factor and act as the recipients.
Function
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,
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 in
The first DNA
See also
References
- ISBN 978-0333194362.
- ISBN 9780199204625.
- ^ PMID 12855161.
- PMID 3027040.
- ^ PMID 37592747.
- ^ 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." See http://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. Retrieved 2023-07-14.
- ^ "Historical Notes About Fertility Factor F (version A)". www.esthermlederberg.com. Retrieved 2023-07-14.
- ^ PMID 23632276.
- ISBN 978-0-07-352526-6.
- PMID 9917389.
- PMID 14633993.