Sigmavirus

A genus of viruses in the family Rhabdoviridae

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Electron micrograph of a rhabdovirus virion
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Sigmavirus is a genus of viruses in the family Rhabdoviridae. This genus is known for infecting insects, particularly Drosophila species. Sigmaviruses are characterized by their bullet-shaped virions and their negative-sense single-stranded RNA genomes.

Structure

Sigmaviruses, like other members of the Rhabdoviridae family, have a distinctive bullet-shaped morphology. The virion is enveloped and contains a helical nucleocapsid. The genome is a single molecule of negative-sense RNA, approximately 12,000 nucleotides in length. The genome encodes five proteins: the nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G), and the large protein (L), which is the RNA-dependent RNA polymerase.

Replication

The replication cycle of sigmaviruses begins with the attachment of the virion to the host cell surface via the glycoprotein (G). Following entry into the host cell, the viral RNA is released into the cytoplasm. The RNA-dependent RNA polymerase (L protein) transcribes the viral genome into mRNA, which is then translated into viral proteins. The nucleoprotein (N) encapsidates the viral RNA, forming the nucleocapsid. Assembly of new virions occurs in the cytoplasm, and mature virions bud from the host cell, acquiring their envelope from the host cell membrane.

Host and Transmission

Sigmaviruses primarily infect Drosophila species, such as Drosophila melanogaster. Transmission of sigmaviruses occurs vertically, from parent to offspring, through the germline. This mode of transmission ensures that the virus is passed on to the next generation of hosts.

Pathogenicity

Sigmaviruses are generally not pathogenic to their insect hosts. However, they can influence the host's susceptibility to environmental factors, such as exposure to carbon dioxide, which can induce paralysis in infected flies. This phenomenon is often used as a diagnostic tool to identify infected individuals.

Research and Applications

Sigmaviruses serve as a model system for studying virus-host interactions, particularly in the context of vertical transmission and host adaptation. They are also used in evolutionary biology to understand the dynamics of host-pathogen coevolution.

Also see

• Rhabdoviridae
• Drosophila
• Virus replication
• RNA virus