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. 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 (backwards). The new DNA is then incorporated into the host cell genome by an integrase enzyme, at which point the retroviral DNA is referred to as a provirus. The host cell then treats the viral DNA as part of its own genome, transcribing and translating the viral genes along with the cell's own genes, producing the proteins required to assemble new copies of the virus. Many retroviruses cause serious diseases in humans, other mammals, and birds.
The term viral protein refers to both the products of the genome of a virus and any host proteins incorporated into the viral particle. Viral proteins are grouped according to their functions, and groups of viral proteins include structural proteins, nonstructural proteins, regulatory proteins, and accessory proteins. Viruses are non-living and do not have the means to reproduce on their own, instead depending on their host cell's machinery to do this. Thus, viruses do not code for most of the proteins required for their replication and the translation of their mRNA into viral proteins, but use proteins encoded by the host cell for this purpose.
Metaviridae is a family of viruses which exist as Ty3-gypsy LTR retrotransposons in a eukaryotic host's genome. They are closely related to retroviruses: members of the family Metaviridae share many genomic elements with retroviruses, including length, organization, and genes themselves. This includes genes that encode reverse transcriptase, integrase, and capsid proteins. The reverse transcriptase and integrase proteins are needed for the retrotransposon activity of the virus. In some cases, virus-like particles can be formed from capsid proteins.
Caulimoviridae is a family of viruses infecting plants. There are 94 species in this family, assigned to 11 genera. Viruses belonging to the family Caulimoviridae are termed double-stranded DNA (dsDNA) reverse-transcribing viruses i.e. viruses that contain a reverse transcription stage in their replication cycle. This family contains all plant viruses with a dsDNA genome that have a reverse transcribing phase in their lifecycle.
Mardivirus is a genus of viruses in the order Herpesvirales, in the family Herpesviridae, in the subfamily Alphaherpesvirinae. Chickens, turkeys, and quail serve as natural hosts. There are six species in this genus. Diseases associated with this genus include: Marek's disease, which causes asymmetric paralysis of one or more limbs, neurological symptoms, and development of multiple lymphomas that manifest as solid tumors. Gallid herpesvirus 2 is the only one of these viruses known to be pathogenic and due to the antigenic similarity between the three viruses the other two have been used to vaccinate against Marek's disease. These viruses have double stranded DNA genomes with no RNA intermediate.
Rous sarcoma virus (RSV) is a retrovirus and is the first oncovirus to have been described. It causes sarcoma in chickens.
The murine leukemia viruses are retroviruses named for their ability to cause cancer in murine (mouse) hosts. Some MLVs may infect other vertebrates. MLVs include both exogenous and endogenous viruses. Replicating MLVs have a positive sense, single-stranded RNA (ssRNA) genome that replicates through a DNA intermediate via the process of reverse transcription.
Human foamy virus (HFV) is a retrovirus and specifically belongs to the genus Spumavirus. The spumaviruses are complex and significantly different from the other six genera of retroviruses in several ways. The foamy viruses derive their name from the characteristic ‘foamy’ appearance of the cytopathic effect (CPE) induced in the cells. Foamy virus in humans occurs only as a result of zoonotic infection.
Simian foamy virus (SFV) is a species of the genus Spumavirus that belongs to the family of Retroviridae. It has been identified in a wide variety of primates, including prosimians, New World and Old World monkeys, as well as apes, and each species has been shown to harbor a unique (species-specific) strain of SFV, including African green monkeys, baboons, macaques, and chimpanzees. As it is related to the more well-known retrovirus human immunodeficiency virus (HIV), its discovery in primates has led to some speculation that HIV may have been spread to the human species in Africa through contact with blood from apes, monkeys, and other primates, most likely through bushmeat-hunting practices.
Group-specific antigen, or gag, is the polyprotein that contains the core structural proteins of an Ortervirus. It was named as such because scientists used to believe it was antigenic. Now it is known that it makes up the inner shell, not the envelope exposed outside. It makes up all the structural units of viral conformation and provides supportive framework for mature virion.
The gag-onc fusion protein is a general term for a fusion protein formed from a group-specific antigen ('gag') gene and that of an oncogene ('onc'), a gene that plays a role in the development of a cancer. The name is also written as Gag-v-Onc, with "v" indicating that the Onc sequence resides in a viral genome. Onc is a generic placeholder for a given specific oncogene, such as C-jun..
Env is a viral gene that encodes the protein forming the viral envelope. The expression of the env gene enables retroviruses to target and attach to specific cell types, and to infiltrate the target cell membrane.
Avian sarcoma leukosis virus (ASLV) is an endogenous retrovirus that infects and can lead to cancer in chickens; experimentally it can infect other species of birds and mammals. ASLV replicates in chicken embryo fibroblasts, the cells that contribute to the formation of connective tissues. Different forms of the disease exist, including lymphoblastic, erythroblastic, and osteopetrotic.
Mason-Pfizer monkey virus (M-PMV), formerly Simian retrovirus (SRV), is a species of retroviruses that usually infect and cause a fatal immune deficiency in Asian macaques. The ssRNA virus appears sporadically in mammary carcinoma of captive macaques at breeding facilities which expected as the natural host, but the prevalence of this virus in feral macaques remains unknown. M-PMV was transmitted naturally by virus-containing body fluids, via biting, scratching, grooming, and fighting. Cross contaminated instruments or equipment (fomite) can also spread this virus among animals.
Human endogenous retrovirus K (HERV-K) or Human teratocarcinoma-derived virus (HDTV) is a family of human endogenous retroviruses associated with malignant tumors of the testes. Phylogenetically, the HERV-K group belongs to the ERV2 or Class II or Betaretrovirus-like supergroup. Over the past several years, it has been found that this group of ERVs play an important role in embryogenesis, but their expression is silenced in most cell types in healthy adults. The HERV-K family, and particularly its subgroup HML-2, is the youngest and most transcriptionally active group and hence, it is the best studied among other ERVs. Reactivation of it or anomalous expression of HML-2 in adult tissues has been associated with various types of cancer and with neurodegenerative diseases such as amytrophic lateral sclerosis (ALS). Endogenous retrovirus K (HERV-K) is related to mammary tumor virus in mice. It exists in the human and cercopithecoid genomes. Human genome contains hundreds of copies of HERV-K and many of them possess complete open reading frames (ORFs) that are transcribed and translated, especially in early embryogenesis and in malignancies. One notable location of HERV-K is the C4 gene of RCCX module. HERV-K is also found in apes and Old World monkeys. It is uncertain how long ago in primate evolution the full-length HERV-K proviruses which are in the human genome today were created.
Positive-strand RNA viruses are a group of related viruses that have positive-sense, single-stranded genomes made of ribonucleic acid. The positive-sense genome can act as messenger RNA (mRNA) and can be directly translated into viral proteins by the host cell's ribosomes. Positive-strand RNA viruses encode an RNA-dependent RNA polymerase (RdRp) which is used during replication of the genome to synthesize a negative-sense antigenome that is then used as a template to create a new positive-sense viral genome.
Bovine foamy virus (BFV) is a ss(+)RNA retrovirus that belongs to the genus spumaviridae. Spumaviruses differ from the other six members of family retroviridae, both structurally and in pathogenic nature. Spumaviruses derive their name from spuma the latin for "foam". The 'foam' aspect of 'foamy virus' comes from syncytium formation and the rapid vacuolization of infected cells, creating a 'foamy' appearance.
Feline foamy virus or Feline syncytial virus is a retrovirus and belongs to the family Retroviridae and the subfamily Spumaretrovirinae. It shares the genus Felispumavirus with only Puma feline foamy virus. There has been controversy on whether FeFV is nonpathogenic as the virus is generally asymptomatic in affected cats and does not cause disease. However, some changes in kidney and lung tissue have been observed over time in cats affected with FeFV, which may or may not be directly affiliated. This virus is fairly common and infection rates gradually increase with a cat's age. Study results from antibody examinations and PCR analysis have shown that over 70% of felines over 9 years old were seropositive for Feline foamy virus. Viral infections are similar between male and female domesticated cats whereas in the wild, more feral females cats are affected with FeFV.
Equine foamy virus (EFV), also called foamy virus (FV), is virus in the genus Equispumavirus. It shares similarities, with respect to replication, with lentiviruses. EFV, along with other FVs are from the family Retroviridae and subfamily Spumaretrovirinae. Spumarivuses, such as EFV, are complicated retroviruses that have been characterized in many animals including nonhuman primates, cattle, cats. Additionally, these viruses have been identified in animals that most often carry lentiviruses.
Ortervirales is an order that contains all accepted species of single-stranded RNA viruses that replicate through a DNA intermediate and all accepted species of double-stranded DNA viruses that replicate through an RNA intermediate . The name is derived from the reverse of retro.
