Using the RNP complex as template, the L protein catalyzes transcription and replication with its RNA-dependent RNA polymerase (RdRp) activity and also caps and methylates the 5′ ends of the viral mRNA transcripts 8, 9.Ītomic structures from x-ray crystallography and cryogenic electron microscopy (cryo-EM) are available for all five VSV proteins 3, 5, 6, 10, 11, 12, 13, 14, 15, 16.

Multiple copies of L, a polyfunctional RNA polymerase, are tethered by their P cofactor to the interior of the helical RNP. Projecting from the membrane are trimeric glycoproteins (G), which mediate host cell attachment and low pH-induced membrane fusion 5, 6, 7. The VSV RNP complex assembles, together with M, into a helical, bullet-shaped structure, as it buds through the plasma membrane of an infected cell 4. All of these proteins are present in mature, infectious virions, in which the negative-strand, genomic RNA is coated with the N protein (one N per 9 ribonucleotides) to form a ribonucleoprotein (RNP) complex 3. The viral genome comprises a regulatory 3′ terminal leader region and 5 genes in the following order: N (nucleoprotein), P (phosphoprotein), M (matrix protein), G (glycoprotein) and L (large polymerase), and a 5′ terminal trailer region. The study of vesicular stomatitis virus (VSV), a prototypic mammalian rhabdovirus, has contributed to our fundamental understanding of the biology of NNS RNA viruses 1, 2. Non-segmented, negative-strand (NNS) RNA viruses of the order Mononegavirales include such human pathogens as Ebola virus, respiratory syncytial virus (RSV), measles virus, and rabies virus (RABV). Together with published structures of recombinant N in various states, our results suggest a mechanism for membrane-coupled self-assembly of VSV and its relatives. Radial inter-layer subunit contacts are fixed within single RNA-N-M1-M2 modules, but flexible lateral and axial interactions allow assembly of polymorphic virions. Two layers of matrix (M) protein link the RNP with the membrane.

The ribonucleoprotein (RNP), genomic RNA complexed with nucleoprotein (N), curls into a dome-like structure with about eight gradually expanding turns before transitioning into the regular helical trunk. By compensating for polymorphism among viral particles with computational classification, we obtained a reconstruction of the shaft (“trunk”) at 3.5 Å resolution, with lower resolution for the rounded tip. We report the structure of intact, infectious VSV particles determined by cryogenic electron microscopy. Both have characteristic bullet-like shapes.

Vesicular stomatitis virus (VSV) is a negative-strand RNA virus with a non-segmented genome, closely related to rabies virus.

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