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Molecular Biology

Genome: The Rhabdoviridae genome is single stranded, negative sense.

Virion Morphology: Helical, bullet-shaped, enveloped virion, about 75 nm wide, and 180 nm long. There are approximately 1,200 molecules of nucleocapsid protein, and about 400 trimeric glycoprotein spikes in the envelope.

Entry7: Rhabdoviridae utilize a variety of receptors for entry into neurons, including the nicotinic acetylcholine receptor. Once the interaction has been made by the virus and its receptor, the virion is endocytosed into the cell.

Replication, Transcription, and Translation7: The processes of replication, transcription, and translation all occur in the cytoplasm. In transcription, there are 5 subgenomic mRNAs. Each mRNA is methylated and phosphorylated by viral enzymes.

All rhabdoviruses encode 5 main genes, located in the following order (although there is some variation between genera) on the genome starting at the 3' end:

N - an RNA binding protein

P - a phosphoprotein and the second subunit of the viral polymerase

M - a matrix protein important for viral assembly

G - a glycoprotein found in the viral envelope

L - the largest protein, and the main subunit of the polymerase

(Note: This gene order is accurate for the Lyssavirus genus. The genus Vesiculovirus codes for a P/C gene in the place of the P gene, and the Ephemerovirus genus encodes for Gns, in addition to a few smaller genes, after the main G gene)7.

Differential gene expression in Rhabdoviridae also reflects this gene order; the further the gene from the 3' end of the template strand, the fewer times it is translated.

Egress7: Rhabdoviridae exit infected cells by budding from the cell membrane.

Rhabdovirus Mutation7: Rhabdoviruses are capable of undergoing rapid evolution. This is due to the high rate of error of their polymerase, and lack of a proof reading function. Combined, these result in an error rate of about 1 in every 104 bases. Because the genomes of rhabdoviridae are only slightly larger than 104 bases, this results in a single base mutation once every round of replication. This ultimately leads to the existence of quasispecies, or populations of virus in the infected host that are closely similar in terms of genetic sequence, but not identical. Consequently, the ability to rapidly evolve allows these viruses to quickly adapt under selective pressures, such as transmission from one species of host to a host of an entirely different species.

Defective Interfering Particles (DIs)7: Rhabdoviridae also generate Defective Interfering Particles, which are generated with the viral polymerase switches from copying one region of the template to copying a different template, or jumping to a different part of the same template. The result is usually a defective genome that interferes with the replication of the standard virus, causing reductions in viral titer.