Microbiology Procedure

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Cloning Organisms

	Cloning Organisms- Various strains of the human colon bacterium Escherichia coli have been used for cloning, they include HBIO1, h303 and RRI. The c1oning organism should preferably be deficient (i.e. recA-) in the major pathway of DNA recombination. This will reduce the possibility of undesirable recombinations. The cloning organism should preferably lack restriction enzymes that might degrade foreign DNA. Such strains are usually also deficient in modification enzymes that protect DNA. Strains that bud off "minicells" are desirable if gene expression (transcription and translation) is the object of study.
The minicells contain plasmids, enzymes and other components required for gene expression, but lack chromosomal DNA. In such a system mRNA or proteins coded by recombinant DNA can be more easily studied as there is no interference from products of chromosomal DNA expression. In eukaryotic cells primary and secondary tissue cultures of the African Green Monkey kidney cells have been used for recombinant DNA experiments. E. coli was the cloning organism for most recombinant DNA studies
In 1974 Fink and his co workers achieved the transplantation of genes from a lower organism into a higher organism when they introduced bacterial DNA into baker's yeast. Yeasts are safer than E.coli for recombinant DNA experiments because they do not live in human beings and are not pathogenic to man. Fink and his co workers introduced the bacterial gene for leucine production into a yeast strain that, was deficient in the ability to produce leucine. A snail enzyme was used for inducing the yeast to take up bacterial DNA.

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