Genus: Dianlovirus

Genus: Dianlovirus

Distinguishing features

Měnglà virus (MLAV) is the only currently classified dianlovirus. Like cuevaviruses, marburgviruses, and possibly ebolaviruses, but unlike striaviruses and thamnoviruses, dianloviruses infect bats. Dianlovirus genomes are highly reminiscent in organization of marburgvirus genomes but contain four rather than only one gene overlap (Yang et al., 2019).

Virion

Morphology

Not reported.

Physicochemical and physical properties

Not reported.

Nucleic acid

Dianlovirus genomes are linear non-segmented RNA molecules of negative polarity. The genomes are about 18.5 kb (Yang et al., 2019). Genomic RNA is likely uncapped and not polyadenylated. 

Proteins

Dianloviruses express seven structural proteins, all of which are homologous to those of cuevaviruses, ebolaviruses, and marburgviruses (Table 1.Dianlovirus). The second most abundant structural protein in virions is assumed to be the nucleoprotein (NP), which encapsidates the dianlovirus genome. The least abundant protein is assumed to be the large protein (L), which mediates dianlovirus genome replication and transcription via its RNA-directed RNA polymerase (RdRP) domain. The dianlovirus ribonucleoprotein (RNP) complex likely consists of NP, RNP complex-associated protein (VP24), polymerase cofactor (VP35), transcriptional activator (VP30), and L. These RNP complexes associate with the matrix protein (VP40), which lines the inner side of the virion membrane and GP1,2, which form globular spikes on the outside of the virion membrane (Yang et al., 2019).

Table 1.Dianlovirus. Location and functions of dianlovirus structural proteins.

Protein (abbreviation)

Encoding gene

Characteristics

Function

References

Nucleoprotein (NP)

1 (NP)

RNP complex component; likely consists of two distinct functional modules; homo-oligomerizes to form helical polymers; binds to genomic and antigenomic RNA, VP35, VP40, VP30, and VP24

Nucleocapsid and cellular inclusion body formation; encapsidation of dianlovirus genome and antigenome; genome replication and transcription

(Yang et al., 2019)

Polymerase cofactor (VP35)

2 (VP35)

RNP complex component; homo‑oligomer; binds to double‑stranded RNA, NP, and L

Replicase‑transcriptase cofactor; inhibits interferon regulatory factor 3 phosphorylation, IFNA1/B1 production, and protein kinase R and PRKRA phosphorylation

(Yang et al., 2019, Williams et al., 2020)

Matrix protein (VP40)

3 (VP40)

Likely consists of two distinct functional modules; homo-oligomerizes to form dimers and circular hexamers and octamers; binds single-stranded RNA, VP35; hydrophobic; membrane‑associated; contains one late‑budding motif; binds NEDD4 and TSG101

Matrix component; regulation of genome transcription and replication; regulation of virion morphogenesis and egress; inhibits JAK‑STAT pathway

(Yang et al., 2019, Williams et al., 2020)

Glycoprotein (GP1,2)

4 (GP)

Type I transmembrane and class I fusion protein; cleaved to GP1 and GP2 subunits that heterodimerize; mature protein is a trimer of GP1,2 heterodimers; inserts into membranes; heavily N- and O‑glycosylated

Virion adsorption to dianlovirus‑susceptible cells via cellular attachment factors; determines dianlovirus cell and tissue tropism; induction of virus‑cell membrane fusion subsequent to endolysosomal binding to NPC1

(Yang et al., 2019)

Transcriptional activator (VP30)

5 (VP30)

RNP complex component; hexameric zinc finger protein; binds single‑stranded RNA, NP, and L

Transcription initiation, reinitiaition, and antitermination

(Yang et al., 2019)

RNP complex-associated protein (VP24)

6 (VP24)

Likely RNP complex component; homo‑tetramerizes; hydrophobic and membrane‑associated

Regulation of genome transcription and replication; regulation of virion morphogenesis and egress

(Yang et al., 2019, Williams et al., 2020)

Large protein (L)

7 (L)

RNP complex component; homo‑dimerizes; binds to genomic and antigenomic RNA, VP35, and VP30; mRNA capping enzyme

Genome replication and mRNA transcription

(Yang et al., 2019)

IFNA1, interferon alpha 1; IFNB1, interferon beta 1; NEDD4, NEDD4 E3 ubiquitin protein ligase; NPC1, NPC intracellular cholesterol transporter 1; PRKRA, protein activator of interferon induced protein kinase EIF2AK2; RNP, ribonucleoprotein; STAT1, signal transducer and activator of transcription 1; TSG101, tumor susceptibility 101; VP, virus protein

Lipids

Not reported.

Carbohydrates

Not reported. 

Genome organization and replication

The dianlovirus genome has the gene order 3′-NP-VP35-VP40-GP-VP30-VP24-L-5′ (Figure 1.Dianlovirus). The undetermined extragenic sequences at the extreme 3′-end (leader) and 5′‑end (trailer) of the genome are assumed to be conserved and to be partially complementary. Genes are flanked by conserved transcriptional initiation and termination (polyadenylation) sites. Four dianlovirus genes overlap (Yang et al., 2019). 

Figure 1.Dianlovirus. Schematic representation of the dianlovirus genome organization. Genome is drawn to scale. Courtesy of Jiro Wada, NIH/NIAID/DCR/IRF-Frederick, Fort Detrick, MD, USA. 

The replication strategy of dianloviruses remains to be studied but is assumed to be highly similar to that of marburgviruses and reminiscent of that of cuevaviruses and ebolaviruses. Dianlovirions are assumed to associate with attachment factors at the plasma membrane that mediate infection by endocytosis. Dianlovirus GP1,2 mediates cell surface C-type lectin binding and subsequent low-pH-dependent fusion into endosomes, followed by GP1,2 binding to the endosomal receptor NPC intracellular cholesterol transporter 1 (NPC1), which is also used by cuevaviruses, ebolaviruses, and marburgviruses. Uncoating is presumed to occur in a manner analogous to that of other mononegaviruses. Dianlovirus transcription and genome replication likely take place in the cytoplasm and, in general, follow the models for members of the families Paramyxoviridae and Pneumoviridae. Transcription starts at the conserved transcriptional initiation site, and polyadenylation occurs at a stretch of uridine residues within the transcriptional termination site. The 5′-terminal non-coding sequences favor hairpin‑like structures for all mRNAs. Replication involves the synthesis of full-length positive-sense copies (antigenomes). During infection, it is assumed that massive amounts of nucleocapsids accumulate intracellularly and form intracytoplasmic inclusion bodies. Virions are likely released via budding from plasma membranes (Figure 3.Filoviridae) (Yang et al., 2019).

Biology

Dianloviruses were discovered in 2019 by high-throughput sequencing of samples taken from an apparently healthy Rousettus sp.) in China (Yang et al., 2019).

Antigenicity

Initial studies indicate that MLAV is antigenically distinct from other filoviruses, but more closely related to marburgviruses than to ebolaviruses (Sherwood and Hayhurst 2019).

Species demarcation criteria

The genus currently includes only a single species.

Member species

Exemplar isolate of the species
SpeciesVirus nameIsolateAccession numberRefSeq numberAvailable sequenceVirus Abbrev.
Mengla dianlovirusMěnglà virusMěnglà virus/Rousettus-wt/CHN/2015/Shārén-Bat9447-1KX371887Complete coding genomeMLAV

Virus names, the choice of exemplar isolates, and virus abbreviations, are not official ICTV designations.

Derivation of names

Dianlovirus: from [diān], an abbreviation denoting China’s Yúnnán Province, and filovirus (Yang et al., 2017).

Related, unclassified viruses 

Virus name

Accession number

Reference

Bat7633A47

MT081488-90

(Paskey et al., 2020)

BtFiloYN2187

KX371877

(Yang et al., 2017)

BtFiloYN2188

KX371878

(Yang et al., 2017)

BtFiloYN2196

KX371880

(Yang et al., 2017)

BtFiloYN2199

KX371881

(Yang et al., 2017)

BtFiloYN2202

KX371882

(Yang et al., 2017)

Virus names and virus abbreviations, are not official ICTV designations.