How a Retrovirus or RNA Virus Works

HIV viruses, illustration

A retrovirus is a virus whose genes are encoded in RNA instead of DNA. Like other viruses, retroviruses need to use the cellular machinery of the organisms they infect to make copies of themselves. However, infection by a retrovirus requires an additional step. The retrovirus genome needs to be reverse-transcribed into DNA  before it can be copied in the usual way. The enzyme that does this backwards transcription is known as reverse transcriptase.

Retroviruses use reverse transcriptase to transform their single-stranded RNA into double-stranded DNA. It is DNA that stores the genome of human cells and cells from other higher life forms. Once transformed from RNA to DNA, the viral DNA can be integrated into the genome of the infected cells. When the DNA versions of the retroviral genes have been incorporated into the genome, the cell then is tricked into copying those genes as part of its normal replication process. In other words, the cell does the work of the virus for it.

Retroviruses are "retro" because they reverse the direction of the normal gene copying process. Usually, cells convert DNA into RNA so that it can be made into proteins. But with retroviruses, the process has to start by going backwards. First, the viral RNA is transformed into DNA. Then the cell can copy the DNA. The cell can also transcribe the DNA back into RNA as the first step in making viral proteins.


The most well-known retrovirus that infects humans is HIV. However, there are several other human retroviruses. These include the human T-cell lymphotropic virus 1 (HTLV-1). HTLV-1 is associated with certain T-cell leukemias and lymphomas. There are many additional retroviruses which have been identified as infecting other species.

HIV treatment is one of the reasons that people have become more familiar with the concept of retroviruses. Reverse transcriptase inhibitors make up some of the well-known classes of HIV drugs. Reverse transcriptase inhibitors prevent HIV from becoming integrated into the genome of the host cell. This, in turn, keeps the cell from making copies of the virus and slows the progression of infection. However, there are growing problems with resistance to many drugs in these classes.

Retroviruses are also sometimes used as gene delivery methods during gene therapy. This is because these viruses are both easy to modify and easily integrated into the host genome. This means that, in theory, they can be used to cause the cellular machinery to make proteins in an ongoing way. For example, scientists have used retroviruses to help diabetic rats make their own insulin. 

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