Negative-sense single-stranded RNA virus
|Negative ssRNA Virus|
|Group:||Group V ((-)ssRNA)|
|Order, Family, and Genus|
A negative-sense single-stranded RNA virus (or (-)ssRNA virus) is a virus that uses negative sense, single-stranded RNA as its genetic material. Single stranded RNA viruses are classified as positive or negative depending on the sense or polarity of the RNA. The negative viral RNA is complementary to the mRNA and must be converted to a positive RNA by RNA polymerase before translation. Therefore, the purified RNA of a negative sense virus is not infectious by itself, as it needs to be converted to a positive sense RNA for replication. These viruses belong to Group V on the Baltimore classification.
Negative sense ssRNA viruses need RNA polymerase to form a positive sense RNA. The positive sense RNA acts as a viral mRNA, which is translated into proteins for the production of new virion materials. With the newly formed virions, more negative sense RNA molecules are produced.
- A virion enters the host cell and releases its negative RNA into the cytoplasm.
- The virus uses its own RNA replicase, also known as RNA-dependent RNA polymerase (RdRp), to form positive RNA template strands through complementary base pairing.
- The positive RNA acts as mRNA, which is translated into structural capsomere proteins and viral RdRp by the host's ribosomes.
- A replicative complex is formed with RdRp: The positive strands can either function as mRNA to produce more proteins or as template to make more negative RNA strands.
- New viral capsids are assembled with the capsomere proteins. The negative RNA strands combine with capsids and viral RdRp to form new negative RNA virions.
- After assembly and maturation of nucleocapsid, the new virions exit the cell by budding or lysing through cell membrane to further infect other cells.
The genome size of a negative RNA virus is between 10kb to 30kb. Two genome subgroups can be distinguished, nonsegmented and segmented, and are described as such:
- In viruses with nonsegmented genomes, the first step of replication is transcription of the negative strand by RdRp to form various monocistronic mRNA that code for individual viral proteins. A positive strand copy is formed to serve as template for the production of the negative genome. This replication takes place in the cytoplasm.
- In viruses with segmented genomes, replication occurs in the nucleus and the RdRp produces one monocistronic mRNA strand from each genome segment. The principal difference between the two types is the location of replication.
One order and eight families are currently recognised in this group. Four of these families contain extremely similar genetic structures and are classified under the order Mononegavirales. A number of unassigned species and genera are yet to be classified.
- Order Mononegavirales
- Unassigned families:
- Unassigned genera:
- Unassigned species:
Viruses of the families Arenaviridae, Orthomyxoviridae, and Paramyxoviridae are able to infect vertebrates. Viruses of the families Bunyaviridae and Rhabdoviridae are able to infect vertebrates, arthropods, and plants. Viruses of the family Tenuivirus only infect plants. A few viruses known to infect humans include Marburg virus, Ebola, measles, mumps, rabies, and influenza.
- Positive-sense single-stranded RNA virus
- Double-stranded RNA virus
- Baltimore classification
- Sense (molecular biology)
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