Protamine

Protamine is a small, arginine-rich, nuclear protein that replaces histone late in the spermiogenesis of some species of fish. Protamines have an amino acid sequence that is rich in arginine and are used in both recombinant DNA technology and in certain types of insulin to prolong the action of the insulin in the body.

Structure

Protamines are rich in arginine and have a high proportion of basic amino acids, which allows them to bind to the negatively charged DNA in the sperm nucleus. This binding compacts the DNA, allowing it to fit within the small sperm head. Protamines are found in the sperm of many species, but not all. For example, in humans, the sperm head is composed of a mixture of histones and protamines.

Function

The primary function of protamines is to replace histones during the process of spermiogenesis. This replacement allows for the DNA to be more tightly packed, which is necessary for the DNA to fit within the small sperm head. In addition to this primary function, protamines also play a role in protecting the DNA from damage.

Clinical significance

Protamines are used in medicine as an antidote to heparin, a blood thinner. They are also used in certain types of insulin to prolong the action of the insulin in the body. In recombinant DNA technology, protamines are used to condense DNA to allow it to be packaged into viral vectors for gene therapy.

See also

• Histone
• Spermiogenesis
• Recombinant DNA
• Insulin

References

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Protamine

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