Hygromycin B is an antibiotic produced by Streptomyces hygroscopicus that inhibits protein synthesis and is used in recombinant cloning to select cells with desired DNA sequences. It is an aminoglycoside antibiotic that affects mRNA translation and is resistant to some bacteria. The hygromycin B resistance gene is used as a selectable marker in cloning experiments to ensure cells contain the desired gene.
Hygromycin B is an antibiotic that is used in recombinant cloning to select cells that have been transformed with a desired DNA sequence. It works to kill sensitive untransformed cells by inhibiting protein synthesis. This compound can be used in cell cultures of bacteria, fungi, plants and mammals. Produced by the soil-dwelling actinomycete Streptomyces hygroscopicus, hygromycin B is also added to raw materials for chickens and pigs to prevent them from being infested with parasites such as worms.
Actinomycetes are a type of bacteria that are common soil dwellers. They produce a variety of natural products that are toxic to other organisms to help them compete and survive in the soil. Many different types of antibiotics have been isolated from these organisms, including streptomycin and actinomycin. Hygromycin B was discovered in 1953. Although it was toxic to humans, its first uses were to boost the feed of poultry and pigs to prevent worm infestation.
Hygromycin B is an example of the aminoglycoside class of antibiotics. It is made up of sugars that have amino groups on them. Several types of bacteria have been found to have resistance to this antibiotic. This resistance is activated by the transfer of a phosphate group to a hydroxyl group—OH— on the antibiotic molecule. The protein that performs this reaction is known as hygromycin B phosphotransferase (Hph).
The mechanism of action of hygromycin B is to inhibit protein synthesis by affecting the translation of messenger RNA (mRNA). Proteins are made up of long chains of amino acids. Normally, ribosomes move along an mRNA strand and form an amino acid according to a set of three mRNA bases known as a codon. When the antibiotic is present, the ribosomes do not read the codon correctly and translate poorly. Generally, this results in the cessation of protein synthesis.
With the advent of recombinant DNA technology, scientists have been able to clone the Hph genes from different types of bacteria. One type of gene has been found in the actinomycete that produces the antibiotic, and another has been found in the gram-negative bacteria Escherichia coli (E. coli) and Klebsiella pneumoniae. Because E. coli is so commonly manipulated in genetic engineering, its gene is the one most commonly used in experiments. The mode of action of this antibiotic is different from many others, often allowing it to be used in combination with another type of antibiotic.
This hygromycin B resistance gene is widely used as a selectable marker during cloning experiments. Thus, it is used on a recombinant plasmid that also contains a gene that scientists wish to introduce into an organism such as a fungus or plant cell line. Only a few cells in a large mixture of cells will generally have the desired plasmid. When an antibiotic is added to the cell mix, it will kill sensitive cells that have not taken up the recombinant plasmid. This selection of hygromycin B ensures that the remaining cells will continue to contain the gene of interest.
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