10 Things to Remember About Retroviruses

1. Retroviruses are the only viruses that have been proven to permanently exist in the human genome, without causing clinical infection. At one point in time, these “endogenous retroviruses” integrated themselves into the germ line of the human race where they now remain, waiting to be passed on to subsequent generations. In fact, approximately 8% of the human genome is comprised of endogenous human retroviruses. Compared with the 1.5% of the human genome that is currently known to encode all necessary human proteins, having 8% of the human genome as human retrovirus sequence is quite amazing.
2. Retroviruses contain the virally encoded enzyme reverse transcriptase, which is a characteristic shared only by one other virus family (Hepadnaviridae). This enzyme, unlike any other polymerase, has the ability to violate the Central Dogma of Biology (DNA to RNA to protein) by synthesizing DNA from viral RNA. This process of making DNA from RNA is backwards, or in reverse, compared with all other forms of transcription…hence the name, reverse transcriptase.
3. All human retroviruses are T-cell lymphotropic, meaning that they prefer to infect the T cell components of the immune system. This characteristic of preferring to invade the cells of the immune system is typical of few other viruses, namely Dengue Virus and Epstein-Barr Virus.
4. Retroviruses contain another unique enzyme by the name of integrase, which is the enzyme responsible for integrating the provirus (DNA form of the virus) into the host’s genome.
5. Not only do retroviruses have the ability to integrate their proviral form into the host genome, this integration has proven to be mandatory and required in order to ensure viral replication and ultimately, the survival of the virus.
6. Retroviruses are the only human viruses that are diploid, meaning that they bring in two identical copies of their RNA genome upon infecting a host cell.
7. One retrovirus in particular, HIV, is responsible for approximately 2.1 million deaths in the year 2007 alone due to the HIV/AIDS pandemic.
8. Currently, there is no vaccine available for any retrovirus.
9. Retroviruses have the ability to maintain a persistent infection despite constant immune surveillance.
10. Retroviruses are currently being used to as gene delivery vectors, specifically to deliver therapeutic genes efficiently and cleanly into cells.