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A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. [2] After invading a host cell's cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome, the reverse of the usual pattern, thus retro (backward).
However, there is a key difference between retroviruses and retrotransposons, which is indicated by the env gene. Although similar to the gene carrying out the same function in retroviruses, the env gene is used to determine whether the gene is retroviral or retrotransposon.
There are two types of oncogenic retroviruses: acute transforming viruses and non-acute transforming viruses. Acute transforming viruses induce a rapid tumor growth since they carry viral oncogenes in their DNA/RNA to induce such growth. An example of an acute transforming virus is the Rous Sarcoma Virus (RSV) that carry the v-src oncogene.
The replication cycle of a retrovirus entails the insertion ("integration") of a DNA copy of the viral genome into the nuclear genome of the host cell.Most retroviruses infect somatic cells, but occasional infection of germline cells (cells that produce eggs and sperm) can also occur.
While there are significant differences in sequence of the env gene between retroviruses, the gene is always located downstream of gag, pro, and pol. The env mRNA must be spliced for expression. The mature product of the env gene is the viral spike protein, which has two main parts: the surface protein (SU) and the transmembrane protein (TM).
A number of satellite viruses—viruses that require the assistance of another virus to complete their life cycle—are also known. Their taxonomy has yet to be settled. The following four genera have been proposed for positive sense single stranded RNA satellite viruses that infect plants— Albetovirus , Aumaivirus , Papanivirus and ...
At the onset of a virus, it’s very difficult to tell the difference between the three respiratory viruses, which all typically present like a cold in the first few days, said Dr. Sameer Kamath ...
Identical LTR sequences at either end of a retrotransposon. A long terminal repeat (LTR) is a pair of identical sequences of DNA, several hundred base pairs long, which occur in eukaryotic genomes on either end of a series of genes or pseudogenes that form a retrotransposon or an endogenous retrovirus or a retroviral provirus.