Plasmids are small, circular pieces of DNA that can be found in prokaryotic cells. They can be naturally occurring or artificially created, and they can carry genes that are not found in the host cell's genome. Plasmids can be used to express genes in prokaryotes in a number of ways.
One way to express a plasmid-borne gene is to use a promoter. A promoter is a sequence of DNA that binds to RNA polymerase, the enzyme that initiates transcription. When RNA polymerase binds to a promoter, it begins to transcribe the gene, which produces a messenger RNA (mRNA) molecule. The mRNA is then translated into a protein by ribosomes.
Another way to express a plasmid-borne gene is to use a transcription factor. A transcription factor is a protein that binds to a specific sequence of DNA and regulates the transcription of genes. When a transcription factor binds to a DNA sequence, it can either increase or decrease the rate of transcription of the gene.
Plasmid-borne gene expression can be used for a variety of purposes, including:
Producing proteins for research or industrial purposes
Engineering bacteria to produce new products or to perform new functions
Developing vaccines or other medical treatments
Plasmid-borne gene expression is a powerful tool that can be used to manipulate the genetic makeup of prokaryotic cells. This technology has the potential to revolutionize the way we produce food, develop new medicines, and protect the environment.
Here are some additional points about plasmid borne gene expression in prokaryotes:
The copy number of a plasmid can affect the level of gene expression.
The host cell's environment can also affect the level of gene expression.
Plasmids can be used to transfer genes between different prokaryotic cells.
Plasmids can be used to create new strains of bacteria with desired properties.
2. PLASMID BORNE GENE
EXPRESSION IN PROKARYOTES
What is plasmid ?
Plasmids are the extra chromosomal
circular DNA.
Found mostly on the bacteria
But some yeast species also have this
plasmid and thus used as a vector in
the gene transfer.
pBR322 plasmid of E.coli
3. GENE EXPRESSION
Generally the gene expression means that gene carried
by the DNA performs some specific function
Eukaryotes
In general in the transcripted
hn-RNA is processed
And the m-RNA is formed
Transcription at nucleus and
translation at the cytoplasm
And is finally translated with the
help of the ribosomes
Animation of eukaryotic gene
regulation
Prokaryotes
The transcription and translation
is coupled
No processing of the m-RNA is
taking place
Both the transcription and the
translation occurs at the
cytoplasm
Animation of prokaryotic gene
regulation
5. General functions of plasmid
The plasmid DNA aids the organism's survival.
It kills other host cells by producing toxic proteins
Protects its own cells by developing resistance to the foreign
materials or antibiotics
The plasmid also aids in the replication of bacterial DNA under
adverse conditions.
Acts as a vector in the gene transfer
Eg: Agrobacterium tumefaciens
6. What is plasmid borne gene
expression ?
The plasmids in the bacteria carry the genes in which it
comprises of several segments
Those segments expresses (translate) to synthesis
proteins
Those translated proteins perform such functions which
may either be beneficial or deleterious to the bacterial
species (Mostly beneficial)
This is called as plasmid borne gene expression
7. Plasmid of E.coli pBR 322
In this plasmid the segment of the gene named as ampR and tetR (expressing segments)
is expressed to produce the protein substances
Those protein substances provides resistance against the antibiotics Ampicilin and
Tetracilin respectively
Meanwhile the mode of action of Tetracyclin is Inhibition of the binding of the
Aminoacetyl t-RNA synthetase at the S-7 protein at the peptidyl site and collapse the
topography of the small ribosomes
The mode of action of Ampilicilin is inhibition of cellwall synthesis (β lactam group of
antibiotics)
8. Staphylococcus aurens
Staphylococcus aurens mainly affects on humans and
causes severe disease on the roots of Arabidopsis
thaliana (Thale cress)
The plasmid of S.aurens bears Methicilin resistant
genes (MRSA) and this MRSA has a large Sccmcc gene
and this further encodes PBp2a protein
The PBp2a protein makes the bacterium resistant to all
sorts of (β lactam group of antibiotics) by making the host
low affinity to β lactams
As the mode of action of β lactam group of antibiotics
affecting the cross murein linkage
Culture of S.aurens Arabidopsis
9. Pseudomonas actinidiae
Twenty-eight strains of Pseudomonas syringae pv. actinidiae isolated in 1984,
1987 and 1988 from kiwifruit orchards in Japan were tested for their
resistance to copper sulfate.
All strains isolated in 1984 were copper sensitive with a minimum inhibitory
concentration (MIC) of cupric sulfate of 0.75 mM
However, some strains isolated in 1987 and 1988 were resistant, with the MIC
ranging from 2.25 to 3.0 mM
All copper-resistant strains contained at least one of two plasmids, pPaCul
(about 70.5 kb) or pPaCu2 about 280 kb or both.
In a copper-resistant strain Pa429, the location of the copper-resistance
genes was examined by insertional inactivation with Tn5.
Tn5 tranposase is a bacterial enzyme (catalytic protein) obtained that
inserts a foreign DNA in bacterial genome
11. Pathogens Plants affected Location
Erwinia amylovora Apple, pear Israel
Lebanon
New Zealand
U.S.(California)
Idaho
Michigan
Missouri
Oregon
Washington
Pseudomonas cichorii celery U.S.(Florida)
Pseudomonas syringae Apple, pear,
ornamental and
landscape trees
New Zealand
U.S.(New York)
Georgia
Michigan
Ohio
Oklahoma
Oregon Washington
Xanthomonas campestris Tomato, pepper Argentina
Brazil
Taiwan
Tonga
U.S.
(California)
Florida
Georgia
Ohio
Pennsylvania
