Retrovirus is a type of virus that contains RNA associated with the enzyme reverse transcriptase as genetic material.
Viruses can be classified according to their genome, consisting of DNA or RNA, in single or double, linear or circular, positive or negative polarity.
In 1971, American microbiologist David Baltimore proposed the following classes to order viruses according to the viral genome:
- Class I: double stranded DNA
- Class II: single stranded DNA
- Class III: RNA double strand
- Class IV: RNA single positive strand
- Class V: RNA single negative strand
- Class VI: RNA single positive strand with an intermediate DNA
- Class VII: Double stranded DNA with intermediate RNA
Retroviruses are viruses of the Retroviridae family and are included in Class VI of the Baltimore classification.
These viruses are part of the first group of viruses discovered in 1904. The human T-lymphotropic virus (HTLV), which targets T lymphocytes, was the first isolated human retrovirus in 1980. It belongs to the same family as the HIV virus.
The best known example of a retrovirus is the HIV virus , which causes AIDS.
Reverse Transcriptase
What characterizes a retrovirus is the presence of the enzyme reverse transcriptase . This enzyme is capable of transforming the single strand of RNA into a double strand of DNA. This is a unique feature of the retrovirus, because, generally, the transformation occurs from DNA to RNA (Transcription).
The retroviral DNA produced is associated with the host cell’s chromosomal DNA.
With the formation of DNA, the RNA strand is degraded. However, the DNA produced by the reverse transcriptase will also synthesize the new RNA that will constitute the genome of the new viruses formed in the infected cell.
Diseases caused by retroviruses
Retroviruses are associated with some diseases in humans. The main ones are AIDS and some types of cancer.
AIDS : The HIV virus attacks T lymphocytes in the blood, the body’s defense cells. As a result, AIDS comprises a set of symptoms and infections resulting from damage to the immune system.
Cancer: Some retroviruses have oncogen genes, they induce host cells to multiply without control, causing tumors.