Caulimoviridae
Encyclopedia
General overview
The Caulimoviridae are a family of virusVirus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es, including the following genera:
- Genus Badnavirus; type species: Commelina yellow mottle virus
- Genus Caulimovirus; type species: Cauliflower mosaic virusCauliflower mosaic virusCauliflower mosaic virus is the type member of the caulimoviruses, one of the six genera in the Caulimoviridae family, pararetroviruses that infect plants...
- Genus Tungrovirus; type species: Rice tungro bacilliform virusRice tungro bacilliform virusRice tungro bacilliform virus is a plant pararetrovirus of the family Caulimoviridae. Tungro means 'degenerated growth' and was first observed in Philippines.-Virology:...
- Genus Soymovirus; type species: Soybean chlorotic mottle virusSoybean chlorotic mottle virusSoybean chlorotic mottle virus is a plant pathogenic virus of the family Caulimoviridae.-External links:**...
- Genus Cavemovirus; type species: Cassava vein mosaic virusCassava vein mosaic virusCassava vein mosaic virus is a plant pathogenic virus of the family Caulimoviridae.-External links:**...
- Genus PetuvirusPetuvirusThe genus Petuvirus belongs to the family Caulimoviridae and is classified under group VII DNA reverse transcribing viruses.Petuviruses are plant viruses. Their genome is unsegmented and monopartite containing a double-stranded DNA molecule that forms an open circle...
; type species: Petunia vein clearing virus
Virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es belonging to the Caulimoviridae family are termed DNA reverse-transcribing viruses (or pararetroviruses) i.e. viruses that contain a reverse transcription stage in their replication cycle. This family contains all plant viruses that consist of a double-stranded DNA genome.
Virus particle structure
All viruses of this family are unenveloped. Virus particles contain nucleocapsids one of two forms; either bacilliform or isometric. The type of nucleocapsid incorporated into the virus structure determines the size of the virus. Bacilliform nucleocapsid viruses are approximately 35-50 nm diameter and can be 900 nm in length. Isometric nucleocapsid viruses are on average 45-50 nm in diameter and show icosahdral symmetry.Genome structure and replication
The genomes of viruses from this family contain monopartite, double-stranded DNA in either an open circular or linear structure. The size of the genome is usually between 6000-8000 base pairs. Depending on the virus, DNA can contain either one open reading frame (ORF) as observed in PetuvirusPetuvirus
The genus Petuvirus belongs to the family Caulimoviridae and is classified under group VII DNA reverse transcribing viruses.Petuviruses are plant viruses. Their genome is unsegmented and monopartite containing a double-stranded DNA molecule that forms an open circle...
es, or up to eight ORFs such as in the Soymoviruses. Proteins found to be encoded in this virus family genome include reverse transcriptase
Reverse transcriptase
In the fields of molecular biology and biochemistry, a reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase enzyme that transcribes single-stranded RNA into single-stranded DNA. It also helps in the formation of a double helix DNA once the RNA has been reverse...
, protease
Protease
A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein....
s, nucleocapsids and transactivators - there are other proteins essential for replication that have yet to be assigned a specific function.
Replication takes place in both the cytoplasm and nucleus of host cells. Firstly, the viral genome enters the cytoplasm
Viral entry
Viral entry is the earliest stage of infection in the viral life cycle, as the virus comes into contact with the host cell and introduces viral material into the cell. The major steps involved in viral entry are shown below. Despite the variation among viruses, the generalities are quite similar...
. The viral DNA forms supercoiled mini-chromosome structures upon entering the host nucleus. The viral DNA is transcribed into polyadenylated RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
which is terminally redundant (due to transcription occurring twice for some parts of the DNA). Newly transcribed RNA enters the cytoplasm once more where it has two roles. It can either be used as a template for viral protein synthesis, or it can undergo reverse transcription by viral encoded reverse transcriptase
Reverse transcriptase
In the fields of molecular biology and biochemistry, a reverse transcriptase, also known as RNA-dependent DNA polymerase, is a DNA polymerase enzyme that transcribes single-stranded RNA into single-stranded DNA. It also helps in the formation of a double helix DNA once the RNA has been reverse...
to make dsDNA. This DNA can then reenter the nucleus for amplification.
As replication requires the use of RNA intermediate, viruses from the Caulimoviridae family are not true dsDNA viruses - instead they are termed DNA reverse-transcribing viruses. As this property is also found in retrovirus
Retrovirus
A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. The DNA is then incorporated into the host's genome by an integrase enzyme. The virus thereafter replicates as part of the host cell's DNA...
es, these families have been compared. However, there are several important differences between retroviruses and viruses from the Caulimoviridae family. Unlike retroviruses, they do not require the integration of viral genome into the host's in order to replicate and for this reason their genome does not encode the enzymatic protein integrase
Integrase
Retroviral integrase is an enzyme produced by a retrovirus that enables its genetic material to be integrated into the DNA of the infected cell...
.
Although they do not regularly integrate into the host genome, sequences from certain Caulimoviridae, such as Petunia vein clearing virus and Banana streak virus
Banana streak virus
Banana streak virus is a plant pathogenic virus of the family Caulimoviridae.-External links:**...
have been found in host genomes. These are termed Endogenous Pararetroviruses, or EPRVs.