Parvoviruses are small non-enveloped, icosahedral DNA viruses with a diameter of 18–26 nm that encapsidate a single-stranded genome of approximately (~)5–6 kb. To date, there are a number of parvoviruses known to infect humans, including adeno-associated viruses (AAVs), parvovirus B19 (B19V), and two newly identified human parvoviruses, which are the human bocavirus (HBoV) and human parvovirus 4 (PARV4).
HBoV was firstly identified in respiratory samples from children with lower respiratory tract infections and subsequently proven epidemiologically to be associated with the diseases. PARV4 was initially found in a blood sample from an intravenous drug user with acute viral infection syndrome. Subsequently, the PARV4 genome was detected in human plasma pools at a low titer. PARV4 had also been found in the livers of hepatitis C virus-positive individuals and the bone marrow of HIV-positive individuals. Recently, PARV4 DNA was detected in cerebrospinal fluid of two children with encephalitis of unknown etiology – however, the disease association of PARV4 remains unclear.
HBoV has been classified as a member in the genus Bocavirus based on the similarity of its genome sequence with those of the two animal bocaviruses. However, the known PARV4 incomplete genome, which lacks information of the terminal repeats, does not show a close relationship to any of the known parvoviruses in the genera of the family Parvoviridae that have been classified to date. This has led to the proposed classification of the PARV4 and PARV4-like viruses as members in a new genus called Partetravirus in the family Parvoviridae by the International Committee on Taxonomy of Viruses (ICTV).
Little is known about the gene expression of PARV4 and the function of PARV4 proteins. Since the PARV4 has not been cultured in vitro, and the full-length genome with terminal repeats has not been sequenced, researchers profiled the gene expression of PARV4 by transfecting a replication-competent PARV4 genome. This study has revelealed for the first time the detailed transcription map of PARV4, which can be beneficial for subsequent study of PARV4 infection.
Molecular characterization of the newly identified human parvovirus 4 in the family Parvoviridae. Virology. Oct 30 2011
Human parvovirus 4 (PARV4) is an emerging human virus, and little is known about the molecular aspects of PARV4 apart from its incomplete genome sequence, which lacks information of the termini. We analyzed the gene expression profile of PARV4 using a nearly full-length HPV4 genome in a replication competent system in 293 cells. We found that PARV4 utilizes two promoters to transcribe non-structural protein- and structural protein-encoding mRNAs, respectively, which were polyadenylated at the right end of the genome. Three major proteins, including the large non-structural protein NS1a, whose mRNA is spliced, and capsid proteins VP1 and VP2, were detected. Additional functional analysis of the NS1a revealed its capability to induce cell cycle arrest at G2/M phase in ex vivo-generated human hematopoietic stem cells. Taken together, our characterization of the molecular features of PARV4 suggests that PARV4 represents a new genus in the family Parvoviridae.