Retroviruses are viruses that have RNA as genetic material. They belong to the Retroviridae family of retroviruses. Once a cell is infected, its RNA is converted to DNA by reverse transcription.
That viral DNA is then incorporated into the DNA of the host cell where it begins to reproduce. For example, human immunodeficiency virus (HIV).
Structure
Retrovirus Meaning – This is a group of RNA viruses that insert a DNA copy of their genome into a host cell to reproduce.
This lipid bilayer consists of two overlapping outer rings with embedded envelope protein complexes. Capsid proteins are hexagonal. Copies of the RNA genome are in the form of loops linked by nucleoproteins.
Retrovirus Replication
↓ The virus infects a normal cell
Viral RNA introduced in the host cell
↓ Reverse Transcription
Viral DNA produced by Reverse Transcriptase
↓
Viral genetic material enters the nucleus of the host cell
↓
Viral DNA integrates into the host genome
↓
Viral genes are transcribed and translated
↓
New virus particles assemble and come out of host cell
↓
New viruses can infect other cells
Vectors
Retroviral vectors are genetically modified retroviruses. They have been used for genetic engineering in mammalian host cells for over 20 years.
Retroviral vectors derived from Moloney murine leukemia virus are the most common retroviruses.
They can easily integrate into the host cell genome and reproduce. Therefore, they have been used as vectors in various gene therapies.
Retroviral vectors are constructed by replacing gag, pol, and env genes with therapeutic genes.
One limitation of the use of retroviral vectors in gene therapy is that the integrase enzyme can introduce genetic material into the native genome of the host cell and this causes genetic disruption.
Examples
HIV attacks the human immune system. It destroys the CD4 T cells responsible for fighting infection. Thus, the immune system becomes weaker.
It can be transmitted through needles, bodily fluids, and from mother to child during childbirth or breastfeeding. It cannot be cured by medicine and treatment. AIDS is the final stage of HIV infection and there is no cure.
The first and second types are closely related. HTLV I infection develops acute T-cell leukemia. It affects the spine and causes nerve problems.
It was the first human retrovirus to be identified and can be transmitted through blood transfusions, needle sharing, breast milk or sexual contact. HTLV II is associated with neurological diseases and some types of leukemia. However, very little is known about this type of virus.
Endogenous retroviruses are a genetic phenomenon of extinct viruses with a similar genetic makeup to extant retroviruses.
Those viruses have been passed on to humans evolving over the years. They make up 5% of the human genome and are passed down from one generation to the next.
