Endogenous retrovirus

Endogenous retroviruses (ERVs) are viral sequences that have been integrated into the genome of an organism. They are remnants of ancient retroviral infections that have been passed down from generation to generation. ERVs make up a significant portion of the genome in many species, including humans.

Overview

ERVs are formed when a retrovirus infects a germ cell, the cells responsible for passing genetic information to offspring. The retrovirus uses an enzyme called reverse transcriptase to convert its RNA into DNA, which is then integrated into the host cell's genome. If the infected germ cell goes on to form a viable organism, the retroviral DNA will be part of the organism's own genome and can be passed on to its offspring.

Classification

ERVs are classified based on their sequence similarity to known retroviruses. In humans, there are three main classes of ERVs: HERV-K, HERV-W, and HERV-L. Each class is further divided into families based on sequence similarity.

Role in Disease

While most ERVs are silent and do not produce any proteins, some can become activated and contribute to disease. For example, ERVs have been implicated in several human diseases, including cancer, autoimmune disease, and neurological disorders. However, the exact role of ERVs in disease is still a topic of ongoing research.

Role in Evolution

ERVs are a significant source of genetic variation and have played a role in evolution. They can influence gene expression and contribute to the evolution of new genes. Some ERVs have been co-opted by their host organisms and now perform beneficial functions. For example, a protein produced by an ERV is essential for the formation of the placenta in mammals.

See Also

• Retrovirus
• Genome
• Reverse transcriptase
• Germ cell

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