Semotivirus is the only genus of viruses in the familyBelpaoviridae (formerly included in the familyMetaviridae).[1] Species exist asretrotransposons in aeukaryotic host's genome. BEL/pao transposons are only found in animals.Semotivirus is the only genus currently recognized, the genus description corresponds to the family,Belpaoviridae description.[2]
The lonegenus in the family,Semotivirus, was formerly included in theMetaviridae family but was removed due to its paraphyletic relationship to otherMetaviridae genera. There is a good chance that more species and genera will be added to the familyBelpaoviridae in the future, given the diversity of belpaovirids that is already recognized. The Pol domain order of the familiesBelpaoviridae,Metaviridae, andRetroviridae is the same within the orderOrtervirales, however theintegrase is either lacking in the case of theCaulimoviridae or positioned upstream of theprotease domain in the case of thePseudoviridae.[3]
The genus is made up of long terminal repeat (LTR) retrotransposons, also referred to as metazoan-infecting reverse transcriptase viruses.[4]
Thegenomic arrangement of members of theBelpaoviridae family is similar to that of long terminal repeat (LTR) retrotransposons of the Metaviridae family.[5] The entire genome is 4.2–10 kb, and one to three genes (pol, env, and gag) are flanked by LTRs of 0.2–1.2 kb.[6] A non-coding region that represents the initial segment of the reverse-transcribed genome is located downstream of the 5′-LTR. This is followed by an 18 nt primer-binding site that is complementary to a certain area inside the 3′-end of a host tRNAArg or a tRNAGly.
Priming the synthesis of the proviral DNA strand is a polypurine tract of approximately 10 nt located upstream of the 3′-LTR. Gag and Pol polyproteins can be encoded by one continuous gene or by two overlapping genes.[7] These genes encode the capsid and nucleocapsid domains, as well as the protease, reverse transcriptase (RT), ribonuclease H, and integrase domains.
Few information is known about the virion morphology of belpaovirids. The virion morphology of semotivirus is poorly understood. However, belpaovirids most likely replicate by forming virus-like particles (VLPs), just like retrovirids, metavirids, and pseudovirids do, since they encode a Gag polyprotein withnucleocapsid and capsid protein domains homologous to those of other members of the order Ortervirales.[8][9] An env-likegene is present in certain belpaovirids, however its exact role is still unknown.[10]
Although the details of replication are not well known, it is thought to resemble that of members of theMetaviridae family,[11] in which RT mediates the conversion of a full transcript into a dsDNA that is incorporated into the host genome by the integrase protein. After the integrated provirus has been transcribed by the host RNA polymerase II, new virus RNAs are created, which the matching host enzymes cap and polyadenylate. Once in the host cell'scytoplasm, these fresh viral RNAs are translated into immature VLPs by Gag and Pol. VLP maturation is the end outcome of the viral protease'sproteolytic processing of the polyproteins. The new viral RNAs are then reverse-transcribed by RT into dsDNA molecules, which are then sent back to the nucleus and inserted into fresh locations within the host cell genome.[12]
Data related toSemotivirus at Wikispecies