In this article we will discuss about the structure of rabies viruses (explained with diagram).
Rhabdo-viruses have a unique bullet-shaped appearance measuring about 180 × 75 nm. They have an envelope with prominent spikes on surface but not very variable in appearance. Spikes are made up of G protein that haem-agglutinate RBCs. The envelope is lined by the matrix protein and contains the nucleocapsid (RNA + N protein) which wound helically inside the core.
The rabies genome encodes five proteins such as nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G) and polymerase (L). Two non-structural proteins (L and NS) are associated with the nucleocapsid and act in concert as the viral polymerase. All rhabdo-viruses have two major structural components: a surrounding envelope and a helical ribonucleoprotein core (RNP).
In the RNP, genomic RNA is tightly encased by the nucleoprotein. Two other viral proteins, the phospoprotein and the large protein (L-protein or polymerase) are associated with the RNP. The glycoprotein forms approximately 400 trimeric spikes which are tightly arranged on the surface of the virus.
The M protein is associated both with the envelope and the RNP, and may be the central protein of rhabdo-virus assembly. The basic structure and composition of rabies virus are shown in Fig. 17.31 A. The concentric layers i.e. envelope membrane bilayer, M protein and tightly coiled encased genomic RNA, are observed in the cross-sectional of the virion (B).
Genome is mono-partite, linear and single stranded RNA consisting of 11,000-15,000 nucleotides. Genomic nucleic acid is usually negative sense or positive sense (hairpin RNA forms are also found).
At 3′-terminus nucleotide sequences are inverted and complementary to similar regions on the 5′ end; but 3′ terminus has no poly (A) tract. The 5′ terminus has a triphosphate. Encapsidated nucleic acid is mainly genomic. Each virion contains full length or shorter copies.
There are about 50 nucleotide long ‘leader’ region at the 3′ end and about 60 non-translated regions at the 5′ end of the (-) sense vRNA. There is a conserved polyadenylation signal at the end of each gene and a short intergenic region between each of the 5 genes.
Most of the information of Rhabdo-viruses comes from Vesicular Stomatitis Virus (VSV) which is very similar to rabies virus. Now the whole rabies genome has been cloned, sequenced and expressed.