Bacteria can be added to foreign DNA in different ways, for example By viral infection or by the free DNA is taken up from the environment. In bacteria, there is a type of enzymes, restriction endonucleases, whose task is to cut up and thus defuse the foreign DNA that may come into the cell. Bacterial particular DNA is designed such that it is not attacked by its own restriction system. A long series of such restriction enzymes had been isolated and characterized, and the enzymes have become important tools when it comes to mapping of genes, for example In tumor viruses, and attempts to link genes from different organisms in the test tube. Restriction endonuclease cuts both chains in the DNA, but only in regions where there are precise nucleotide sequences. The sequence is identified, specific to each enzyme.
Pieces from two types of DNA treated with the same restriction enzyme, could be spliced together by another enzyme, a DNA ligase. The principle has been utilized to connect to a foreign genes carry DNA that in turn can be inserted into a suitable host cell where the genes may be reproduced and read. Genes from a pig, for instance. Been transferred in this way to a mutant of the intestinal bacterium Escherichia coli, where they have been reproduced generation after generation.
As the carrier DNA used plasmids, which are small ring-shaped DNA molecules that exist in some bacteria. At certain conditions can free plasmid DNA is taken up by E. coli bacteria and established in it. By special methods of analysis can then strange DNA detected in these cells. In other experiments, the bacterial virus DNA was used as carrier DNA, and to the foreign genes into animal cells used DNA from animal viruses such as transport. This research (recombinant DNA research), which includes the design and creation of new combinations of genes and to study the function of these in a host cell, opens in theory possible to transfer any gene from one organism to another, so unless a suitable self-replicating carrier DNA can be found.
It is also possible to insert genes for the treatment of cells with precipitated DNA, or by injection with a thin glass tube. When DNA is inserted at the last steps in the fertilized muse egg and mouse eggs placed in the mouse uterus, occurs transgenic mice, mice with extra bits of genes in their chromosomes. Pure science has now given methods that allow a more thorough investigation of many biological problems. Using recombinant DNA technique has been discovered that genes in animals and plants are split into coding and non-coding regions. It has revealed a genetic structure of the genes that control the synthesis of immune proteins. It has the DNA pieces that reagent (probe) had been capable to measure the production in the tissues of mRNA from the corresponding genes, and thus able to study, for example. hormonal gene regulation.
By studying the effect of cloned DNA introduced into cells in culture, has been found that DNA-area in front of the gene coding parts, promoter region, is important for initiation of transcription and hormonal regulation of this. It is shown by gradually removing parts of the promoter region. The introduction of cloned genes in muse egg is shown the promoter sequences that ensure that genes come to the right expressions at the exact time and right place in the mouse development. For example. Provide a piece of 205 base pairs in the promoter of pancreatic elastase (an enzyme in the pancreas) for the formation of 500 000 times more elastase in the pancreas than in the kidneys.
Recombinant DNA technology has opened up new opportunities in BIOTECHNOLOGY. Hormones such as insulin, growth hormone and other medically significant proteins are now produced in bacteria, yeast or cells in culture. DNA probes for diagnosis of infectious and genetic diseases is another important application area. Animal and plant genes can be altered by the introduction of new DNA. The use of DNA probes is estimated to follow markers of "good" genetic traits in common breeding. It is also estimated that normal genes can be transferred to people who are sick because they have inherited a defective gene.
Some researchers, however, were concerned. they follow the construction of new organisms with unknown gene combinations can get. That is why in many countries, issued guidelines on equipment and safety measures for different types of test that is graded according to potential danger. Experimental design must be approved by a public body (in law ).
