Leviviruses

Leviviruses are a genus of viruses belonging to the family Leviviridae. These viruses are characterized by their small size, simple structure, and RNA genome. They are bacteriophages, meaning they infect bacteria. Specifically, leviviruses infect Gram-negative bacteria, with their primary hosts being members of the genus *Escherichia*.

The virion, or the complete virus particle, of a levivirus is non-enveloped and has an icosahedral capsid. The capsid is composed of multiple copies of a single structural protein, making it a very efficient way to package the genetic material. The genome is a single-stranded RNA molecule of positive polarity. This means the RNA can directly act as messenger RNA (mRNA) and be translated by the host cell's ribosomes to produce viral proteins.

Replication of leviviruses occurs within the cytoplasm of the host bacterium. Upon infection, the viral RNA is released into the bacterium. The host machinery then transcribes and translates the viral RNA to produce viral proteins, including those for replication and capsid assembly. New virions are assembled and released from the host cell, often through lysis, which kills the bacterium.

Leviviruses are of interest in molecular biology due to their simple genetic organization and replication strategy. They have been valuable tools for studying fundamental processes like RNA replication and protein synthesis. Their genetic material is relatively small, containing only a few genes essential for their life cycle. Examples of viruses in this genus include the MS2 bacteriophage, which is widely used in laboratory research.