Cauliflower mosaic virus
Encyclopedia
Cauliflower mosaic virus (CaMV) is the type member of the caulimoviruses, one of the six genera in the Caulimoviridae
family, pararetroviruses that infect plant
s (Pringle, 1999). Pararetroviruses replicate through reverse transcription just like retrovirus
es, but the viral particles contain DNA
instead of RNA
(Rothnie et al., 1994).
with a diameter of 52 nm built from 420 capsid protein (CP) subunits arranged with a triangulation T = 7, which surrounds a solvent-filled central cavity (Cheng et al., 1992). It contains a circular double-stranded DNA molecule of about 8.0 kB, interrupted by sitespecific discontinuities resulting from its replication by reverse transcription.
After entering
the host, the single stranded nicks in the viral DNA are repaired, forming a supercoiled molecule that binds to histones. This DNA is transcribed into a full length, terminally redundant 35S RNA and a subgenomic 19S RNA.
The 35S RNA is particularly complex, containing a highly structured 600 nucleotide long leader sequence with six to eight short open reading frame
s (ORFs) (Fütterer et al., 1988; Pooggin et al., 1998).
This leader is followed by seven tightly arranged longer ORFs that encode all the viral proteins (reviewed by Hohn and Fütterer, 1997). The mechanism of expression of these proteins is very special. The ORF VI protein (encoded by the 19S RNA) controls translation reinitiation of major open reading frames on the polycistronic 35S RNA, which is normally only happens on bacterial mRNA's. TAV function depends on its association with polysomes and eukaryotic initiation factor eIF3 (Park et al., 2001).
The Cauliflower Mosaic Virus promoter (CaMV 35S) is used in most transgenic crops to activate foreign genes which have been artificially inserted into the host plant. It is inserted into transgenic plants in a form which is different to that found when it is present in its natural brassica plant hosts. This enables it to operate in a wide range of host-organism environments which would otherwise not be possible.
CaMV contains about 8 kb double-strand DNA genome and produces spherical particles. CaMV infections are systemic, and even its DNA is infectious when inoculated on abraded plant surfaces. The CaMV genome has 8 tightly packed genes, of which only two small genes, genes II and VII, are nonessential; as a result, only these two genes can be replaced/deleted without a loss of infectivity. In addition, modified CaMV genomes exceeding the natural genome size (8024 bp) by even a few hundred bp are not packaged into virions. These two factors seriously limit the size of DNA insert clonable in CaMV. Bacterial dhfr (dihydrofolate reductase) gene was inserted in the CaMV genome in place of gene II, and was successfully expressed in plants.
Cauliflower mosaic virus (CaMV) is the type member of the caulimoviruses, one of the six genera in the Caulimoviridae family, pararetroviruses that infect plants (Pringle, 1999). Pararetroviruses replicate through reverse transcription just like retroviruses, but the viral particles contain DNA instead of RNA (Rothnie et al., 1994).
Structure
Caulimoviridae
-General overview:The Caulimoviridae are a family of viruses, including the following genera:*Genus Badnavirus; type species: Commelina yellow mottle virus*Genus Caulimovirus; type species: Cauliflower mosaic virus...
family, pararetroviruses that infect plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s (Pringle, 1999). Pararetroviruses replicate through reverse transcription just like 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, but the viral particles contain DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
instead of RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
(Rothnie et al., 1994).
Structure
The CaMV particle is an icosahedronIcosahedron
In geometry, an icosahedron is a regular polyhedron with 20 identical equilateral triangular faces, 30 edges and 12 vertices. It is one of the five Platonic solids....
with a diameter of 52 nm built from 420 capsid protein (CP) subunits arranged with a triangulation T = 7, which surrounds a solvent-filled central cavity (Cheng et al., 1992). It contains a circular double-stranded DNA molecule of about 8.0 kB, interrupted by sitespecific discontinuities resulting from its replication by reverse transcription.
After entering
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 host, the single stranded nicks in the viral DNA are repaired, forming a supercoiled molecule that binds to histones. This DNA is transcribed into a full length, terminally redundant 35S RNA and a subgenomic 19S RNA.
Genome
The promoter of the 35S RNA is a very strong constitutive promoter responsible for the transcription of the whole CaMV genome. It is well known for its use in plant transformation. It causes high levels of gene expression in dicot plants. However, it is less effective in monocots, especially in cereals. The differences in behavior are probably due to differences in quality and/or quantity of regulatory factors. The promoter was named CaMV 35S promoter ("35S promoter") because the coefficient of sedimentation of the viral transcript, whose expression is naturally driven by this promoter, is 35S. It is one of the most widely used, general-purpose constitutive promoters. It was discovered at the beginning of the 1980s, by Chua and collaborators at the Rockefeller University.The 35S RNA is particularly complex, containing a highly structured 600 nucleotide long leader sequence with six to eight short open reading frame
Open reading frame
In molecular genetics, an open reading frame is a DNA sequence that does not contain a stop codon in a given reading frame.Normally, inserts which interrupt the reading frame of a subsequent region after the start codon cause frameshift mutation of the sequence and dislocate the sequences for stop...
s (ORFs) (Fütterer et al., 1988; Pooggin et al., 1998).
This leader is followed by seven tightly arranged longer ORFs that encode all the viral proteins (reviewed by Hohn and Fütterer, 1997). The mechanism of expression of these proteins is very special. The ORF VI protein (encoded by the 19S RNA) controls translation reinitiation of major open reading frames on the polycistronic 35S RNA, which is normally only happens on bacterial mRNA's. TAV function depends on its association with polysomes and eukaryotic initiation factor eIF3 (Park et al., 2001).
- ORF I - Movement protein
- ORF II - Insect transmission factor
- ORF III - the protein translated shows a non-specific DNA binding activity. it is a structural protein in virus particle.
- ORF IV - Capsid protein
- ORF V - Protease, reverse transcriptase and RNaseH
- ORF VI - Translational activator / Inclusion body protein
- ORF VII - Unknown (dispensable)
Replication
CaMV replicates by reverse transcription. Initially all the gaps present in the genome are sealed and the covalently closed DNA then associates with host histones to form a super coiled mini chromosome. Transcription of this mini chromosome produces 35s RNA which translates protein as well as forming dsDNA by the process of reverse transcription. New viral particles are produced which are targeted to inclusion bodies & are released outside.The Cauliflower Mosaic Virus promoter (CaMV 35S) is used in most transgenic crops to activate foreign genes which have been artificially inserted into the host plant. It is inserted into transgenic plants in a form which is different to that found when it is present in its natural brassica plant hosts. This enables it to operate in a wide range of host-organism environments which would otherwise not be possible.
CaMV contains about 8 kb double-strand DNA genome and produces spherical particles. CaMV infections are systemic, and even its DNA is infectious when inoculated on abraded plant surfaces. The CaMV genome has 8 tightly packed genes, of which only two small genes, genes II and VII, are nonessential; as a result, only these two genes can be replaced/deleted without a loss of infectivity. In addition, modified CaMV genomes exceeding the natural genome size (8024 bp) by even a few hundred bp are not packaged into virions. These two factors seriously limit the size of DNA insert clonable in CaMV. Bacterial dhfr (dihydrofolate reductase) gene was inserted in the CaMV genome in place of gene II, and was successfully expressed in plants.
Cauliflower mosaic virus (CaMV) is the type member of the caulimoviruses, one of the six genera in the Caulimoviridae family, pararetroviruses that infect plants (Pringle, 1999). Pararetroviruses replicate through reverse transcription just like retroviruses, but the viral particles contain DNA instead of RNA (Rothnie et al., 1994).
Structure