Tick-Borne Nyamanini Virus Replicates in the Nucleus and Exhibits Unusual Genome and Matrix Protein Properties

Abstract

Tick-borne Nyamanini virus (NYMV) is the prototypic member of a recently discovered genus in the order Mononegavirales , designated Nyavirus . The NYMV genome codes for six distinct genes. Sequence similarity and structural properties suggest that genes 1, 5, and 6 encode the nucleoprotein (N), the glycoprotein (G), and the viral polymerase (L), respectively. The function of the other viral genes has been unknown to date. We found that the third NYMV gene codes for a protein which, when coexpressed with N and L, can reconstitute viral polymerase activity, suggesting that it represents a polymerase cofactor. The second viral gene codes for a small protein that inhibits viral polymerase activity and further strongly enhances the formation of virus-like particles when coexpressed with gene 4 and the viral glycoprotein G. This suggests that two distinct proteins serve a matrix protein function in NYMV as previously described for members of the family Filoviridae . We further found that NYMV replicates in the nucleus of infected cells like members of the family Bornaviridae . NYMV is a poor inducer of beta interferon, presumably because the viral genome is 5′ monophosphorylated and has a protruding 3′ terminus as observed for bornaviruses. Taken together, our results demonstrate that NYMV possesses biological properties previously regarded as typical for filoviruses and bornaviruses, respectively.

Orchid Fleck Virus Structural Proteins N and P Form Intranuclear Viroplasm-Like Structures in the Absence of Viral Infection

“…Tick-borne Nyamanini virus, a prototypic member of a proposed genus, "Nyavirus," replicates in the nucleus of infected cells like members of the orthomyxoviruses and bornaviruses do (52). Similarly to the N proteins of nucleorhabdoviruses, as stated above, the candidate NLSs in the N protein of Nyamanini and Midway nyaviruses (53) were predicted in our preliminary PSORT analysis (H. Kondo, unpublished result), suggesting that these N proteins also have an important role in the nuclear import of viral RNP (17).…”

Reverse Genetics Identifies the Product of Open Reading Frame 4 as an Essential Particle Assembly Factor of Nyamanini Virus

“…ORF2 was further shown to promote production of infectious virus-like particles by an unknown mechanism (3). Formation of virus-like particles required the simultaneous presence of the viral G protein, the product of ORF4, and the product of ORF2, indicating that ORF2 and ORF4 both play a role in NYMV particle assembly (3). It remains unclear, however, whether ORF4 represents the NYMV-specific equivalent of a matrix protein typically found in negative-strand RNA viruses.…”

“…The viral nucleoprotein N, the glycoprotein G, and the polymerase L are encoded by ORF1, ORF5, and ORF6, respectively. We recently showed that ORF3 codes for a polymerase cofactor which is required for NYMV polymerase activity (3). The functions of the proteins encoded by ORF2 and ORF4 remain largely unknown.…”

“…Recently, Kuhn and coworkers (2) proposed classifying NYMV as a member of a new mononegaviral family, designated "Nyamiviridae." NYMV replicates in the nucleus of infected cells (3), and viral budding was proposed to occur at the plasma membrane (1). The NYMV genome contains six major open reading frames (ORFs).…”

“…The functions of the proteins encoded by ORF2 and ORF4 remain largely unknown. ORF2 negatively regulates NYMV polymerase activity, presumably through interaction with the ORF3 product (3). ORF2 was further shown to promote production of infectious virus-like particles by an unknown mechanism (3).…”