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Paramyxoviruses and Rhabdoviruses
Paramyxoviridae and Rhabdoviridae
Virion
Genome
Genes and proteins
Viruses and hosts
Diseases
Distinctive characteristics
Paramyxoviruses and Rhabdoviruses
Paramyxoviridae and Rhabdoviridae
 Virion
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Paramyxoviruses: spherical, diameter 150–300
nm, also found as filaments.
Rhabdoviruses: bullet-shaped rods, 180 75 nm.
Envelope derived from plasma membrane.
Coiled helical nucleocapsid.
Paramyxoviruses and Rhabdoviruses
Paramyxoviridae and Rhabdoviridae
 Genome
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Linear ssRNA, negative sense.
Single segment.
Paramyxoviruses: 15–18 Kb.
Rhabdoviruses: 11–12 Kb.
Paramyxoviruses and Rhabdoviruses
Paramyxoviridae and Rhabdoviridae
 Genes and proteins
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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:
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Nucleocapsid protein (N)
RNA polymerase cofactor and accessory proteins (P/C/V)
Matrix protein (M)
Fusion protein (F)
Hemagglutinin/neuraminidase,
Paramyxoviruses and Rhabdoviruses
Paramyxoviridae and Rhabdoviridae
 Viruses and hosts
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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
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Rhabdoviruses:
 Humans: rabies virus
 Cattle: vesicular stomatitis virus
 Numerous rhabdoviruses infecting bats, fish, insects,
plants
Paramyxoviruses and Rhabdoviruses
Paramyxoviridae and Rhabdoviridae
 Diseases
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Paramyxoviruses: several important childhood
diseases, including measles, mumps, respiratory
diseases in humans;
 canine distemper, rinderpest.
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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.
Paramyxoviruses and Rhabdoviruses
Paramyxoviridae and Rhabdoviridae
 Distinctive characteristics
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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).
Virion
 The mononegaviruses: a group of related
negative-strand RNA viruses
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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
Virion
 Rabies is a fatal human encephalitis caused
by a rhabdovirus
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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
Virion
 Paramyxovirus and rhabdovirus virions have
distinct morphologies
Structure of paramyxoviruses
Virion
 Paramyxovirus and rhabdovirus virions have
distinct morphologies
Structure of rhabdoviruses
Virion
 Viral envelope proteins are responsible for
receptor binding and fusion with cellular
membranes
Fig. 20.3 Schematic diagram of paramyxovirus virion.
Genome
Fig. 20.4 Envelope proteins of paramyxoviruses.
Genome
 Genome RNA is contained within helical
nucleocapsids
Structure of paramyxovirus helical nucleocapsid
Genome
 Paramyxoviruses enter the cell by fusion with
the plasma membrane at neutral pH
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Binding
 Sendai : HN - sialic acid
 Measles : H - CD46, CD150/SLAM
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Upon binding, F protein undergoes conformational
change that allows insertion of fusion peptide to
plasma membrane.
Genome
 Gene order is conserved among different
paramyxoviruses and rhabdoviruses
Fig. 20.6 Paramyxovirus genome RNA.
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Leader region
 Signals for initiation of RNA synthesis
 Signals for packaging of full-length RNA genome
 No cap, no poly A tail
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Intergenic sequence
 Controls txn termination, polyadenylation, reinitiation
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
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. 20.7 Alternative models for transcription of
mononegavirus genome RNA.
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
Genes and Proteins
Fig. 20.8 Paramyxovirus transcription and replication.
Genes and proteins
 The P/C/V gene codes for several proteins
by using alternative translational starts and
by mRNA “editing”
Fig. 20.9 Sendai virus P/C/V gene: open reading frames,
translational start sites, and “stuttering” site.
Genes and proteins
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Functions of P, C, and V proteins
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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
Genes and proteins
 N protein levels control the switch from
transcription to genome replication
 Virions are assembled at the plasma
membrane
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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.
Key Terms
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B lymphocytes
Coiled-coil
Dendritic cells
Encephalitis
Fusion peptide
Gangliosides
Hemagglutination
Hemagglutinin
Interferon
Nested set
Neuraminidase
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Pseudotyping
Sialic acid
Subacute sclerosing
panencephalitis (SSPE)
Synctia (singular: syncytium)
T lymphocytes
Type I integral membrane
protein
Type II integral membrane
protein