The Paramyxoviridae constitute a large family of single-stranded negative-sense RNA viruses. Members of the family include established human pathogens such as measles and mumps viruses. Most of the characterised paramyxoviruses infect terrestrial vertebrates; however, recent metagenomic studies have led to the discovery of several novel paramyxoviruses infecting marine vertebrates.
The canonical genome of terrestrial vertebrate paramyxoviruses comprises six genes, N / P / M / F / AP / L, arranged in a strict linear sequence. In the novel marine paramyxoviruses, most of these genes are readily identified based on sequence homology and locus. The exception is the P gene, where up to five uncharacterised open reading frames (ORFs) lacking evidence of homology are found at the typical P gene locus between the N and M genes.
In terrestrial vertebrate paramyxoviruses, the P gene can encode a number of proteins through mechanisms that include co-transcriptional mRNA editing and the use of alternative translational start sites. However, in all cases, the P gene encodes the phosphoprotein, a multifunctional scaffold protein essential for viral replication. The phosphoprotein is found in complex with the L protein, the catalytic subunit of the viral polymerase, and consists of interspersed structured and unstructured regions. The structured elements are a centrally located coiled-coil responsible for homo-oligomerisation and a C-terminal three-helix bundle with binding activities that enable transcription and genome replication. Additionally, an intrinsically disordered region at the N-terminus of the phosphoprotein plays a vital role in the packaging of viral RNA into the viral nucleocapsid.
Here, based on key structural and functional traits, we present evidence that supports the classification of one uncharacterised ORF in Wēnlǐng tonguesole paramyxovirus (WTSPV) as a phosphoprotein analogue.