1. Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae
Virion
Genome
Genes and proteins
Viruses and hosts
Diseases
Distinctive characteristics

2. Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae
Virion
Paramyxoviruses: spherical, diameter 150–300 nm, also found as filaments.
Rhabdoviruses: bullet-shaped rods, nm.
Envelope derived from plasma membrane.
Coiled helical nucleocapsid.

3. Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae
Genome
Linear ssRNA, negative sense.
Single segment.
Paramyxoviruses: 15–18 Kb.
Rhabdoviruses: 11–12 Kb.

4. Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae
Genes and proteins
Five to nine genes, transcribed in series from 3 end of genome by viral RNA polymerase.
Most genes produce a single mRNA and a single protein.
Most proteins packaged in virion:
Nucleocapsid protein (N)
RNA polymerase cofactor and accessory proteins (P/C/V)
Matrix protein (M)
Fusion protein (F)
Hemagglutinin/neuraminidase,

5. Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae
Viruses and hosts
Paramyxoviruses:
Humans: measles, mumps, respiratory syncytial, parainfluenza viruses
Animals: viruses infecting birds, pigs, dogs, cats, seals, whales, etc., Sendai (mice), Newcastle disease (chickens), canine distemper, rinderpest (cattle) viruses
Rhabdoviruses:
Humans: rabies virus
Cattle: vesicular stomatitis virus
Numerous rhabdoviruses infecting bats, fish, insects, plants

6. Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae
Diseases
Paramyxoviruses: several important childhood diseases, including measles, mumps, respiratory diseases in humans;
canine distemper, rinderpest.
Emerging paramyxoviruses Hendra and Nipah cause respiratory and neurological disease in pigs, humans, horses, and bats.
Rhabdoviruses: rabies (fatal encephalitis in humans), transmitted by bites of infected animals; vesicular stomatitis virus
in cattle. Numerous insect and plant diseases.

7. Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae
Distinctive characteristics
RNA-dependent RNA polymerase in virion transcribes genome into mRNAs.
Single transcriptional promoter at 3 end of RNA; mRNAs made by a start-stop mechanism.
Full-length genome or antigenome RNA is always present as assembled nucleocapsids.
Some paramyxoviruses “edit” P mRNA at a specific site, generating mRNAs with distinct protein-coding capacities.
Some paramyxoviruses induce cell-cell fusion, producing multinucleated cells (syncytia).

8. Virion
The mononegaviruses: a group of related negative-strand RNA viruses
Single RNA genome packaged in a helical nucleocapsid
Envelope derived from host plasma membrane
Viral RNA polymerase packaged in the virion
mRNAs made by a start-stop mechanism

9. Virion Rabies is a fatal human encephalitis caused by a rhabdovirus
Infect wide variety of hosts
Rabies virus is of significant concern to human health
Infected by virus-containing saliva from bites of infected animals
Infection results in a fatal encephalitis
Measles is a serious childhood disease caused by a paramyxovirus

10. Virion
Paramyxovirus and rhabdovirus virions have distinct morphologies
Structure of paramyxoviruses

11. Virion
Paramyxovirus and rhabdovirus virions have distinct morphologies
Structure of rhabdoviruses

12. Virion
Viral envelope proteins are responsible for receptor binding and fusion with cellular membranes
Fig Schematic diagram of paramyxovirus virion.

13. Genome
Fig Envelope proteins of paramyxoviruses.

14. Genome Genome RNA is contained within helical nucleocapsids
Structure of paramyxovirus helical nucleocapsid

15. Genome
Paramyxoviruses enter the cell by fusion with the plasma membrane at neutral pH
Binding
Sendai : HN - sialic acid
Measles : H - CD46, CD150/SLAM
Upon binding, F protein undergoes conformational change that allows insertion of fusion peptide to plasma membrane.

16. Genome
Gene order is conserved among different paramyxoviruses and rhabdoviruses
Leader region
Signals for initiation of RNA synthesis
Signals for packaging of full-length RNA genome
No cap, no poly A tail
Intergenic sequence
Controls txn termination, polyadenylation, reinitiation
Fig Paramyxovirus genome RNA.

17. Genes and Proteins
Viral messenger RNAs are synthesized by an RNA polymerase packaged in the virion
Viral RNA polymerase initiates transcription exclusively at the 3’ end of the viral genome

18. Genes and Proteins
(a) Multiple-promoter model: RNA polymerases (gray spheres) initiate transcription
independently at promoters just upstream of each viral gene.
(b) Single entry model: RNA polymerases initiate transcription only at the 3 end of the genome,
Fig Alternative models for transcription of mononegavirus genome RNA.

19. Genes and Proteins
The promoter for plus-strand RNA synthesis consists of two sequence elements separated by one turn of the ribonucleoprotein helix
mRNAs are synthesized sequentially from the 3 to the 5 end of the genome RNA

20. Genes and Proteins
Fig Paramyxovirus transcription and replication.

21. Genes and proteins
The P/C/V gene codes for several proteins by using alternative translational starts and by mRNA “editing”
Fig Sendai virus P/C/V gene: open reading frames, translational start sites, and “stuttering” site.

22. Genes and proteins Functions of P, C, and V proteins
P : cofactor required for viral RNA synthesis
directs binding of L to the promoter
V : not normally required for replication
interferes with host mechanisms that reduce
viral replication
C : required for formation of infectious virion
exact roles not understood

23. Genes and proteins
N protein levels control the switch from transcription to genome replication
Virions are assembled at the plasma membrane
Envelope protein inserted into plasma membrane
Matrix protein associates with cytoplasmic face of p.m.
Nucleocapsid interact w/ matrix protein
Virions are made by budding from p.m.

25. Key Terms Pseudotyping B lymphocytes Sialic acid Coiled-coil
Subacute sclerosing panencephalitis (SSPE)
Synctia (singular: syncytium)
T lymphocytes
Type I integral membrane protein
Type II integral membrane protein
B lymphocytes
Coiled-coil
Dendritic cells
Encephalitis
Fusion peptide
Gangliosides
Hemagglutination
Hemagglutinin
Interferon
Nested set
Neuraminidase