Family: Pseudoviridae

Genus: Hemivirus

Distinguishing features

As for members of the genus Pseudovirus, hemiviruses encode Gag and Pol proteins in one or two reading frames. The mechanism(s) that regulates Gag and Gag-Pol expression for most single ORF viruses remain to be determined, but for Drosophila melanogaster copia virus (DmecopiaV), Gag proteins are encoded on a spliced 2 kb mRNA, and regulation occurs by differential splicing. The primer for minus-strand DNA synthesis during reverse transcription, unlike for members of the families Retroviridae and Metaviridae, or of the genus Pseudovirus is initiator tRNA^Met half-molecule, or a tRNA^Arg half-molecule in the case of other elements such as Candida albicans Tca2 virus (CalTca2V). This tRNA fragment is generated by cleaving the initiator tRNA in the anticodon stem.

Virion

See discussion under family description. 

Genome organization and replication

The genome of DmecopiaV is 5,165 nt, including a 276 nt 5′-long terminal repeat (LTR) and a 277 nt 3′-LTR. The internal region contains a primer binding site (PBS) for the tRNA^Met primer (Kikuchi et al., 1986), a single ORF of 1,409 codons and a polypurine tract (PPT) preceding the 3′-LTR. The ORF encodes the typical Gag-Pol polyprotein containing the Gag, protease (PR), integrase (INT) and reverse transcriptase-ribonuclease H (RT-RH) domains. Both Gag and Gag-Pol primary translation products are processed by the cognate protease into final products. The known gag-encoded proteins include analogs of retroviral capsid (CA) and nucleocapsid (NC) proteins. The known pol-encoded proteins include PR, INT and RT-RH. All of these proteins appear to be required for replications. 

Biology

Hemiviruses are found worldwide in fungi, algae and insect genomes, but not in plants. Their mode of transmission is unknown although presumed to be through vertical inheritance. 

Species demarcation criteria

See discussion under family description.