The gag-onc fusion protein
is a general term for a
fusion protein
Fusion proteins or chimeric (kī-ˈmir-ik) proteins (literally, made of parts from different sources) are proteins created through the joining of two or more genes that originally coded for separate proteins. Translation of this ''fusion gene'' r ...
formed from a
group-specific antigen
Group-specific antigen, or gag, is the polyprotein that contains the core structural proteins of an Ortervirus (except ''Caulimoviridae''). It was named as such because scientists used to believe it was antigenic. Now it is known that it makes up ...
('gag') gene and that of an
oncogene
An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels. ('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
Transcription factor Jun is a protein that in humans is encoded by the ''JUN'' gene. c-Jun, in combination with protein c-Fos, forms the AP-1 early response transcription factor. It was first identified as the Fos-binding protein p39 and only lat ...
. (In the case of a fusion with C-jun, the resulting "gag-jun" protein is known alternatively as
p65).
Background
Gag genes are part of a general architecture for
retroviruses
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. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase e ...
, viruses that replicate through
reverse transcription
A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, ...
, where the gag region of the
genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
encodes proteins that constitute the matrix, capsid and nucleocapsid of the mature virus particles. Like in
HIV's replication cycle, these proteins are needed for
viral budding
Viral shedding is the expulsion and release of virus progeny following successful reproduction during a host (biology), host cell (biology), cell infection. Once replication has been completed and the host cell is exhausted of all resources in ma ...
from the host cell's plasma membrane, where the fully formed
virion
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's 1 ...
s leave the cell to infect other cells.
gag-v-onc
When a viral gene is introduced into the host cell and is sufficient to induce oncogenesis – the creation of cancerous cells – in the infected cell line, the gene is said to be a "viral transforming gene".
When this type of gene is
translated
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
to a protein, the protein is called a "transforming protein". Note that since the viral oncogenes originated from a host genome, the transformation event is different from
transduction, which describes the process of introducing non-native genes to a host organism via a viral infection.
Rous sarcoma virus
The Gag-v-Onc fusion protein from the
Rous sarcoma virus illustrates the dual role that the fusion protein plays in the viral and host cellular life cycle. For example, the viral gene
Src (as in "sarcoma") is not necessary for viral reproduction, but does affect
virulence
Virulence is a pathogen's or microorganism's ability to cause damage to a host.
In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ca ...
. Due to evidence
of conserved
homology
Homology may refer to:
Sciences
Biology
*Homology (biology), any characteristic of biological organisms that is derived from a common ancestor
* Sequence homology, biological homology between DNA, RNA, or protein sequences
*Homologous chrom ...
between the
v-Src
v-Src is a gene found in Rous sarcoma virus (RSV) that encodes a tyrosine kinase that causes a type of cancer in chickens.
The src gene is oncogenic as it triggers uncontrolled growth in abnormal host cells. It was the first retroviral oncogene ...
gene and its host (animal) genomes, and its non-essential status for viral reproduction, the v-Src gene is likely to have been acquired from a host genome and altered by subsequent mutations. These subsequent mutations are responsible for the oncogenic capabilities of the virus, as the normal (host) version of the Src gene,
c-Src
Proto-oncogene tyrosine-protein kinase Src, also known as proto-oncogene c-Src, or simply c-Src (cellular Src; pronounced "sarc", as it is short for sarcoma), is a non-receptor tyrosine kinase protein that in humans is encoded by the ''SRC'' gene ...
promotes survival,
angiogenesis
Angiogenesis is the physiological process through which new blood vessels form from pre-existing vessels, formed in the earlier stage of vasculogenesis. Angiogenesis continues the growth of the vasculature by processes of sprouting and splitting ...
,
proliferation and invasion pathways. These native pathways are disrupted in the presence of the mutant Src gene (v-Src) such that
oncogenesis
Carcinogenesis, also called oncogenesis or tumorigenesis, is the formation of a cancer, whereby normal cells are transformed into cancer cells. The process is characterized by changes at the cellular, genetic, and epigenetic levels and abnor ...
becomes more likely for the infected host cells, since the v-Src gene is
translated
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
into a functionally distinct version of its host counterpart.
murine leukemia virus
In the case of the
murine leukemia virus
The murine leukemia viruses (MLVs or MuLVs) 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 pos ...
es, a species of viruses capable of causing cancer in
murine
The Old World rats and mice, part of the subfamily Murinae in the family Muridae, comprise at least 519 species. Members of this subfamily are called murines. In terms of species richness, this subfamily is larger than all mammal families excep ...
s (mice), the viral life cycle can also be responsible for oncogenesis through a Gag-v-Onc fusion protein called "Mo-MuLV(src)", which is a Gag-v-Src protein capable of inducing oncogenesis in living mice.
See also
*
Rous sarcoma virus
*
Fusion protein
Fusion proteins or chimeric (kī-ˈmir-ik) proteins (literally, made of parts from different sources) are proteins created through the joining of two or more genes that originally coded for separate proteins. Translation of this ''fusion gene'' r ...
*
Fusion gene A fusion gene is a hybrid gene formed from two previously independent genes. It can occur as a result of translocation, interstitial deletion, or chromosomal inversion. Fusion genes have been found to be prevalent in all main types of human neopla ...
*
Fusion transcript Fusion transcript is a chimeric RNA encoded by a fusion gene or by two different genes by subsequent trans-splicing. Certain fusion transcripts are commonly produced by cancer cells, and detection of fusion transcripts is part of routine diagnostics ...
*
Chimeric gene
Chimeric genes (literally, made of parts from different sources) form through the combination of portions of two or more coding sequences to produce new genes. These mutations are distinct from fusion genes which merge whole gene sequences into ...
*
Bcr-abl fusion protein
The Philadelphia chromosome or Philadelphia translocation (Ph) is a specific genetic abnormality in chromosome 22 of leukemia cancer cells (particularly chronic myeloid leukemia (CML) cells). This chromosome is defective and unusually short becaus ...
*
Oncovirus
An oncovirus or oncogenic virus is a virus that can cause cancer. This term originated from studies of acutely transforming retroviruses in the 1950–60s, when the term "oncornaviruses" was used to denote their RNA virus origin. With the lette ...
*
Retrovirus
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. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase ...
*
Retrotransposon
Retrotransposons (also called Class I transposable elements or transposons via RNA intermediates) are a type of genetic component that copy and paste themselves into different genomic locations (transposon) by converting RNA back into DNA through ...
*
Retroposon
Retroposons are repetitive DNA fragments which are inserted into chromosomes after they had been reverse transcribed from any RNA molecule.
Difference between retroposons and retrotransposons
In contrast to retrotransposons, retroposons never ...
*
Integrase
Retroviral integrase (IN) is an enzyme produced by a retrovirus (such as HIV) that integrates—forms covalent links between—its genetic information into that of the host cell it infects. Retroviral INs are not to be confused with phage int ...
External links
*
* http://www.ijbs.com/v06p0730.htm#headingA7
References
{{Viral proteins
Viral protein class
Viral oncoproteins
Biochemistry
Cell biology