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recombinant DNA

 
Dictionary: recombinant DNA
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n.
Genetically engineered DNA prepared by transplanting or splicing genes from one species into the cells of a host organism of a different species. Such DNA becomes part of the host's genetic makeup and is replicated.


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Genetics Encyclopedia: Recombinant DNA
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Recombinant DNA refers to a collection of techniques for creating (and analyzing) DNA molecules that contain DNA from two unrelated organisms. One of the DNA molecules is typically a bacterial or viral DNA that is capable of accepting another DNA molecule; this is called a vector DNA. The other DNA molecule is from an organism of interest, which could be anything from a bacterium to a whale, or a human. Combining these two DNA molecules allows for the replication of many copies of a specific DNA. These copies of DNA can be studied in detail, used to produce valuable proteins, or used for gene therapy or other applications.

The development of recombinant DNA tools and techniques in the early 1970s led to much concern about developing genetically modified organisms with unanticipated and potentially dangerous properties. This concern led to a proposal for a voluntary moratorium on recombinant DNA research in 1974, and to a meeting in 1975 at the Asilomar Conference Center in California. Participants at the Asilomar Conference agreed to a set of safety standards for recombinant DNA work, including the use of disabled bacteria that were unable to survive outside the laboratory. This conference helped satisfy the public about the safety of recombinant DNA research, and led to a rapid expansion of the use of these powerful new technologies.

Overview of Recombination Techniques

The basic technique of recombinant DNA involves digesting a vector DNA with a restriction enzyme, which is a molecular scissors that cuts DNA at specific sites. A DNA molecule from the organism of interest is also digested, in a separate tube, with the same restriction enzyme. The two DNAs are then mixed together and joined, this time using an enzyme called DNA ligase, to make an intact, double-stranded DNA molecule. This construct is then put into Escherichia coli cells, where the resulting DNA is copied billions of times. This novel DNA molecule is then isolated from the E. coli cells and analyzed to make sure that the correct construct was produced. This DNA can then be sequenced, used to generate protein from E. coli or another host, or for many other purposes.

There are many variations on this basic method of producing recombinant DNA molecules. For example, sometimes researchers are interested in isolating a whole collection of DNAs from an organism. In this case, they digest the whole genome with restriction enzyme, join many DNA fragments into many different vector molecules, and then transform those molecules into E. coli. The different E. coli cells that contain different DNA molecules are then pooled, resulting in a "library" of E. coli cells that contain, collectively, all of the genes present in the original organism.

Another variation is to make a library of all expressed genes (genes that are used to make proteins) from an organism or tissue. In this case, RNA is isolated. The isolated RNA is converted to DNA using the enzyme called reverse transcriptase. The resulting DNA copy, commonly abbreviated as cDNA, is then joined to vector molecules and put into E. coli. This collection of recombinant cDNAs (a cDNA library) allows researchers to study the expressed genes in an organism, independent from nonexpressed DNA.

Applications

Recombinant DNA technology has been used for many purposes. The Human Genome Project has relied on recombinant DNA technology to generate libraries of genomic DNA molecules. Proteins for the treatment or diagnosis of disease have been produced using recombinant DNA techniques. In recent years, a number of crops have been modified using these methods as well.

As of 2001, over eighty products that are currently used for treatment of disease or for vaccination had been produced using recombinant DNA techniques. The first was human insulin, which was produced in 1978. Other protein therapies that have been produced using recombinant DNA technology include hepatitis B vaccine, human growth hormone, clotting factors for treating hemophilia, and many other drugs. At least 350 additional recombinant-based drugs are currently being tested for safety and efficacy. In addition, a number of diagnostic tests for diseases, including tests for hepatitis and AIDS, have been produced with recombinant DNA technology.

Gene therapy is another area of applied genetics that requires recombinant DNA techniques. In this case, the recombinant DNA molecules themselves are used for therapy. Gene therapy is being developed or attempted for a number of inherited human diseases.

Recombinant DNA technology has also been used to produce genetically modified foods. These include tomatoes that can be vine-ripened before shipping and rice with improved nutritional qualities. Genetically modified foods have generated controversy, and there is an ongoing debate in some communities about the benefits and risks of developing crops using recombinant DNA technology.

Since the mid-1970s, recombinant DNA techniques have been widely applied in research laboratories and in pharmaceutical and agricultural companies. It is likely that this relatively new area of genetics will continue to play an increasingly important part in biological research into the foreseeable future.

Bibliography

Cooper, Geoffrey. The Cell: A Molecular Approach. Washington, DC: ASM Press, 1997.

Glick, Bernard, and Jack Pasternak. Molecular Biotechnology: Principles and Applications of Recombinant DNA, 2nd ed. Washington, DC: ASM Press, 1998.

Kreuzer, Helen, and Adrianne Massey. Recombinant DNA and Biotechnology, 2nd ed. Washington, DC: ASM Press, 2000.

Lodish, Harvey, et al. Molecular Cell Biology, 4th ed. New York: W. H. Freeman, 2000.

Old, R. W., and S. B. Primrose. Principles of Gene Manipulation, 5th ed. London: Blackwell Scientific Publications, 1994.

Internet Resource

"Approved Biotechnology Drugs." Biotechnology Industry Organization. http://www.bio.org/aboutbio/guide2.html.

—Patrick G. Guilfoile

Sports Science and Medicine: recombinant DNA
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A synthetic form of DNA made by genetic engineering by transplanting genes from one species into the cells of a host organism of a different species. Such DNA becomes part of the host's genetic make-up and is replicated. The recombinant DNA will contain the genetic code for making a particular protein or polypeptide of the donor organism. For example, the human gene for erythropoietin can be transplanted into a bacterium to synthesize recombinant human erythropoietin. When this is injected into the body, it has the same effects as naturally produced erythropoietin, boosting haemoglobin content and improving oxygen carrying capacity of the blood. As recombinant eryrthropoietin has the same chemical structure as natural erythropoietin, it is on the World Anti-Doping Agency Prohibited List.

Biology Q&A: What is recombinant DNA?
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Recombinant DNA is hybrid DNA that has been created from more than one source. An example is the splicing of human DNA into bacterial DNA so that a human gene product is produced by a bacterial cell.

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Wikipedia: Recombinant DNA
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 This article may require cleanup to meet Wikipedia's quality standards. Please improve this article if you can. (April 2009)

Recombinant DNA is a form of DNA that does not exist naturally, which is created by combining DNA sequences that would not normally occur together.[1] In terms of genetic modification, recombinant DNA (rDNA) is introduced through the addition of relevant DNA into an existing organismal DNA, such as the plasmids of bacteria, to code for or alter different traits for a specific purpose, such as antibiotic resistance.[1] It differs from genetic recombination, in that it does not occur through processes within the cell, but is engineered.[1] A recombinant protein is a protein that is derived from recombinant DNA.[2]

The Recombinant DNA technique was first proposed by Peter Lobban, a graduate student with A. Dale Kaiser at the Stanford University Department of Biochemistry. The technique was then realized by Lobban and Kaiser; Jackson, Symons and Berg; and Stanley Norman Cohen, Chang, Herbert Boyer and Helling., in 1972-4. They published their findings in papers including a 1972 paper entitled "Biochemical Method for Inserting New Genetic Information into DNA of Simian Virus 40: Circular SV40 DNA Molecules Containing Lambda Phage Genes and the Galactose Operon of Escherichia coli", a 1973 paper entitled "Enzymatic end-to end joining of DNA molecules" and a 1974 paper entitled "Construction of Biologically Functional Bacterial Plasmids in vitro",[3] all of which described techniques to isolate and amplify genes or DNA segments and insert them into another cell with precision, creating a transgenic bacterium. Recombinant DNA technology was made possible by the discovery, isolation and application of restriction endonucleases by Werner Arber, Daniel Nathans, and Hamilton Smith, for which they received the 1978 Nobel Prize in Medicine. Cohen and Boyer applied for a patent on the Process for producing biologically functional molecular chimeras which could not exist in nature in 1974. The patent was granted in 1980.


Contents

Applications and methods

Cloning and relation to plasmids

Main article: Cloning
A simple example of how a desired gene is inserted into a plasmid. In this example, the gene specified in the white color becomes useless as the new gene is added.

The use of cloning is interrelated with Recombinant DNA in classical biology, as the term "clone" refers to a cell or organism derived from a parental organism,[1] with modern biology referring to the term as a collection of cells derived from the same cell that remain identical.[1] In the classical instance, the use of recombinant DNA provides the initial cell from which the host organism is then expected to recapitulate when it undergoes further cell division, with bacteria remaining a prime example due to the use of viral vectors in medicine that contain recombinant DNA inserted into a structure known as a plasmid.[1]

Plasmids are extrachromosomal self-replicating circular forms of DNA present in most bacteria, such as Escherichia coli (E. Coli), containing genes related to catabolism and metabolic activity,[1] and allowing the carrier bacterium to survive and reproduce in conditions present within other species and environments. These genes represent characteristics of resistance to bacteriophages and antibiotics[1] and some heavy metals, but can also be fairly easily removed or separated from the plasmid by restriction endonucleases,[1], which regularly produce "sticky ends" and allow the attachment of a selected segment of DNA, which codes for more "reparative" substances, such as peptide hormone medications including insulin, growth hormone, and oxytocin. In the introduction of useful genes into the plasmid, the bacteria are then used as a viral vector, which are encouraged to reproduce so as to recapitulate the altered DNA within other cells it infects, and increase the amount of cells with the recombinant DNA present within them.

The use of plasmids is also key within gene therapy, where their related viruses are used as cloning vectors or carriers, which are means of transporting and passing on genes in recombinant DNA through viral reproduction throughout an organism.[1] Plasmids contain three common features -- a replicator, selectable marker and a cloning site.[1] The replicator or "ori"[1] refers to the origin of replication with regard to location and bacteria where replication begins. The marker refers to a particular gene that usually contains resistance to an antibiotic, but may also refer to a gene that is attached alongside the desired one, such as that which confers luminescence to allow identification of successfully recombined DNA.[1] The cloning site is a sequence of nucleotides representing one or more positions where cleavage by restriction endonucleases occurs.[1] Most eukaryotes do not maintain canonical plasmids; yeast is a notable exception.[4] In addition, the Ti plasmid of the bacterium Agrobacterium tumefaciens can be used to integrate foreign DNA into the genomes of many plants. Other methods of introducing or creating recombinant DNA in eukaryotes include homologous recombination and transfection with modified viruses.

Chimeric plasmids

An example of chimeric plasmid formation from two "blunt ends" via the enzyme, T4 Ligase.

When recombinant DNA is then further altered or changed to host additional strands of DNA, the molecule formed is referred to as "chimeric" DNA molecule,[1] with reference to the mythological chimera, which consisted as a composite of several animals.[1] The presence of chimeric plasmid molecules is somewhat regular in occurrence, as, throughout the lifetime of an organism[1], the propagation by vectors ensures the presence of hundreds of thousands of organismal and bacterial cells that all contain copies of the original chimeric DNA.[1]

In the production of chimeric plasmids, the processes involved can be somewhat uncertain[1], as the intended outcome of the addition of foreign DNA may not always be achieved and may result in the formation of unusable plasmids. Initially, the plasmid structure is linearised[1] to allow the addition by bonding of complementary foreign DNA strands to single-stranded "overhangs"[1] or "sticky ends" present at the ends of the DNA molecule from staggered, or "S-shaped" cleavages produced by restriction endonucleases.[1]

A common vector used for the donation of plasmids originally was the bacterium Escherichia coli and, later, the EcoRI derivative[5], which was used for its versatility[5] with addition of new DNA by "relaxed" replication when inhibited by chloramphenicol and spectinomycin, later being replaced by the pBR322 plasmid.[5]In the case of EcoRI, the plasmid can anneal with the presence of foreign DNA via the route of sticky-end ligation, or with "blunt ends" via blunt-end ligation, in the presence of the phage T4 ligase [5], which forms covalent links between 3-carbon OH and 5-carbon PO4 groups present on blunt ends.[5] Both sticky-end, or overhang ligation and blunt-end ligation can occur between foreign DNA segments, and cleaved ends of the original plasmid depending upon the restriction endonuclease used for cleavage.[5]

Synthetic insulin production using recombinant DNA

 This article is written like a personal reflection or essay and may require cleanup. Please help improve it by rewriting it in an encyclopedic style. (April 2009)

One of the biggest breakthroughs in recombinant DNA technology happened in the manufacture of biosynthetic "human" insulin, which was the first medicine made via recombinant DNA technology ever to be approved by the FDA. It was the ideal candidate because it is a relatively simple protein and was therefore relatively easy to copy, it was so widely used that if researchers could prove that biosynthetic "human" insulin was safe and effective, then the technology would be accepted as such, and it would open the flood gates for many other products to be made this way.

The specific gene sequence, or oligonucleotide, that codes for insulin production in humans was introduced to a sample colony of E. coli (the bacteria found in the human intestine). Only about 1 out of 106 bacteria picks up the sequence. However, this is not really a problem, because the lifecycle is only about 30 minutes for E. coli. This means that in a 24-hour period, there may be billions of E. coli that are coded with the DNA sequences needed to induce insulin production.[6]

However, a sampling of initial reaction showed that Humulin was greeted more as a technological rather than a medical breakthrough, and that this sentiment was building even before the drug reached pharmacies.

The Economist concluded: "The first bug-built drug for human use may turn out to be a commercial flop. But the way has now been cleared-and remarkably quickly, too - for biotechnologists with interesting new products to clear the regulatory hurdles and run away with the prizes."[7]

Ultimately, widespread consumer adoption of biosynthetic "human" insulin did not occur until the manufacturers removed highly-purified animal insulin from the market.

See also

Notes

  1. ^ a b c d e f g h i j k l m n o p q r s t u v Jeremy M. Berg, John L. Tymoczko, Lubert Stryer, (2007). Biochemistry. San Francisco: W. H. Freeman. ISBN 0-7167-8724-5. 
  2. ^ The Recombinant Protein Handbook
  3. ^ Cohen SN, Chang AC, Boyer HW, Helling RB (1973). "Construction of biologically functional bacterial plasmids in vitro". PNAS 70 (11): 3240–3244. doi:10.1073/pnas.70.11.3240. PMID 4594039. 
  4. ^ "Plasmids in eukaryotic microbes: an example". http://www.sci.sdsu.edu/~smaloy/MicrobialGenetics/topics/plasmids/yeast-plasmid.html. Retrieved 2007-06-05. 
  5. ^ a b c d e f Nathan P. Kaplan, Nathan P. Colowick, Ray Wu (1980). Recombinant DNA, Volume 68: Volume 68: Recombinant Dna Part F (Methods in Enzymology). Academic Press. ISBN 0-1218-1968-X. 
  6. ^ Human insulin from recombinant DNA technology - Johnson 219 (4585): 632 - Science
  7. ^ Invisible Frontiers: The Race to Synthesize a Human Gene"(1987, Tempus Books of Microsoft Press)

References

  • Garret, R. H.; Grisham, C. M. (2000), Biochemistry, Saunders College Publishers, ISBN 0030758173 .
  • Colowick, S. P.; Kapian, O. N. (1980), Methods in Enzymology - Volume 68; Recombinant DNA, Academic Press, ISBN 012181968X .
  • Inoue, Noboru; Takeuchi, Hideya; Ohashi, Makoto; Suzuki, Takamoto (1995). "The production of recombinant human erythropoietin". Biotechnology Annual Review (Elsevier Science B.V.) 1: 297-300. ISBN 9780444818904. 

External links

  • [1] Herbert W. Boyer, Living history project. Oral history

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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
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