Gyrovirus

The genus contains the following species: • Gyrovirus anas1 • Gyrovirus anas2 • Gyrovirus chauna1 • Gyrovirus chickenanemia (Chicken anemia virus) • Gyrovirus fulgla1 • Gyrovirus galga1 • Gyrovirus galga2 • Gyrovirus homsa1 • Gyrovirus homsa2 • Gyrovirus homsa3 • Gyrovirus homsa4 • Gyrovirus hydho1 • Gyrovirus myferr1 • Gyrovirus phaco1 == Structure ==

Gyroviruses have an average size of 19 to 27 nanometers. They are nonenveloped and have an icosahedral capsid with T=1 symmetry. The unique, single protein, trumpet-shaped capsomeres of Gyrovirus are arranged into 12 pentomers yielding a capsid 60 units in size. The genome is circular, non-segmented, and 2290–2320 nucleotides long. == Genome ==

The Gyrovirus genome consists of negative sense, single-stranded, circular, DNA. The genome is relatively small at 2,300 nucleotides. and contains three overlapping open reading frames that code for only three known proteins. == Proteins ==

The Gyrovirus genome codes for a single polysistronic mRNA that subsequently codes for three proteins, VP1, VP2, and VP3. VP1 is the 51kd capsid protein; in addition to its structural function, it also contains motifs for rolling circle replication in the C-terminal region. VP2 is a 23kd nonstructural protein with phosphatase activity. Virions with mutations in SP2 are still replication competent; however, their cytopathic effects were highly attenuated. VP3, also called apoptin, is a 13kd protein that has been shown to independently induce apoptosis in chicken cells. Apoptin is also being researched for its ability to induce apoptosis in human tumor cells. == Replication strategy ==

Viral replication is nuclear. Entry into the host cell is achieved by penetration into the host cell. DNA-templated transcription, with some alternative splicing mechanism is the method of transcription. The virus exits the host cell by nuclear egress, and nuclear pore export. Birds serve as the natural host. Transmission routes are fecal-oral, parental, egg transmission, and respiratory. == Chicken anemia virus ==

Chicken anemia virus (CAV) was, until 2011, the only member of genus Gyrovirus identified. It causes disease worldwide in areas where chickens are produced. CAV causes severe anemia, hemorrhaging, and depletion of lymphoid tissue through the destruction of bone marrow erythroblastoid cells. A second virus in this genus—Avian gyrovirus 2—has been described. The viral genome shares ~40% of its sequence with Chicken anemia virus (CAV). The genome is 2383 nucleotides long and has three partially overlapping open reading frames encoding the proteins VP1, VP2 and VP3. These proteins share 38.8%, 40.3%, and 32.2% amino acid identities between their homologs in the CAV. Two species have been described from humans—human gyrovirus and human gyrovirus 3. Human gyrovirus 1 appears to be the same virus as avian gyrovirus 2. A fourth gyrovirus—gyrovirus 4 (GyV4)—has been isolated from human stool and chicken meat. == Literature ==