The production and accumulation of the virally encoded

The production and accumulation of the virally encoded proteins signals a switch in the polymerase function, from viral mRNA transcription to genome replication, in which N plays a critical role. An essential step in the viral replication of the nascent positive-sense genome (antigenome) relies on its encapsidation, a process facilitated by cis-acting conserved sequences located on the 3′ ends of viral genome and antigenome (Whelan and Wertz, 1999; Li and Pattnaik, 1999). Additionally, N and P proteins are critical in promoting genome replication, as the N/P complex provides the structural and chaperone support for the nascent RNA to bind via sugar-phosphate interactions to the N protein (Albertini et al., 2006). The bound antigenome will then function as template for the synthesis of encapsidated negative-sense genomes, which will be assembled into progeny virions.
Virion assembly is a staggered process where the various components [nucleocapsid core (RNP), G and M proteins] are sequestered in different cellular compartments and converge in the final steps of the process. The nucleocapsid is assembled during RNA replication in the cytoplasm, as is observed for members of the genera Vesiculovirus, Lyssavirus, Ephemerovirus and Novirhabdovirus. Viral G protein is inserted into the endoplasmic reticulum where chaperones (BiP and calnexin)(Hammond and Helenius, 1994) facilitate its proper folding and assembly into trimers (Doms et al., 1988), prior to transport and fusion into the Golgi complex. As it traffics through the cell it undergoes further posttranslational modifications including glycosylations (Schmidt and Schlesinger, 1979), prior to its transport to cholesterol- and sphingolipid-rich lipid rafts in the baso-lateral plasma membrane. M protein is synthesized mostly as a soluble protein in the KN-93 hydrochloride (McCreedy et al., 1990) and is also membrane bound, albeit at lower amounts (Ogden et al., 1986). However both forms of the M protein are recruited for assembly of nucleocapsid/M complexes at the host plasma membrane from where virions will bud (Odenwald et al., 1986). This budding process is facilitated by the interaction of M with host-encoded proteins responsible for the formation of multivesicular bodies (MVB), and their release from the plasma membrane (Harty et al., 2001).

‘Classical’ vertebrate rhabdoviruses
For historical reasons any reference to classical vertebrate rhabdoviruses denotes members of the genera Vesiculovirus and Lyssavirus, represented by the prototype species vesicular stomatitis Indiana virus (VSIV) and rabies virus (RABV), respectively. Vesiculoviruses have a wide host range among mammals and are transmitted by hematophagous insects (sandflies and/or mosquitoes). Lyssaviruses utilize mostly bats as their principal reservoir hosts as well as various terrestrial carnivores as terminal hosts. Viruses of each genus form a monophyletic clade in a maximum likelihood (ML) tree inferred from complete L protein sequences (Dietzgen et al., 2011; Walker et al., 2015). Structurally both demonstrate the classic rhabdovirus enveloped bullet-shaped virions (Fig. 1) packaging a genome consisting of five genes (3′-N-P-M-G-L-5′), each separated by a short gene junction (intergenic region), and flanked by highly conserved 3′ leader (le) and 5′ trailer (tr) sequences (Fig. 3). In vesiculoviruses the P gene mRNA contains 2 additional alternate start codons that initiate translation at alternative open reading frames (ORFs) that encode two small basic proteins C and C’ (55-aa and 65-aa, respectively) of unknown function (Spiropoulou and Nichol, 1993; Peluso et al., 1996). Suppression of C/C’ expression has no apparent effects in virus replication or pathogenicity in vivo (Kretzschmar et al., 1996). Of note is that not all members of the genus express alternative ORFs in P [e.g. vesicular stomatitis Alagoas, Maraba, Malpais Spring, Morreton viruses] (Walker et al., 2015), and additional ORFs KN-93 hydrochloride (≥150nt) may be present in alternative reading frames in other genes than P (Walker et al., 2015).