paramyxoviruses and rhabdoviruses paramyxoviridae and rhabdoviridae virion genome genes and proteins...
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Paramyxoviruses and RhabdovirusesParamyxoviridae and Rhabdoviridae
VirionVirion
GenomeGenome
Genes and proteinsGenes and proteins
Viruses and hostsViruses and hosts
DiseasesDiseases
Distinctive characteristicsDistinctive characteristics
Virion 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 RhabdovirusesParamyxoviridae and Rhabdoviridae
Genome Linear ssRNA, negative sense. Single segment. Paramyxoviruses: 15–18 Kb. Rhabdoviruses: 11–12 Kb.
Paramyxoviruses and RhabdovirusesParamyxoviridae 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,
Paramyxoviruses and RhabdovirusesParamyxoviridae 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
Paramyxoviruses and RhabdovirusesParamyxoviridae 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.
Paramyxoviruses and RhabdovirusesParamyxoviridae 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).
Paramyxoviruses and RhabdovirusesParamyxoviridae and Rhabdoviridae
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
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
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
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.
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. 20.6 Paramyxovirus genome RNA.
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
Fig. 20.7 Alternative models for transcription of mononegavirus genome RNA.
(a) Multiple-promoter model: RNA polymerases (gray spheres) initiate transcriptionindependently at promoters just upstream of each viral gene.
(b) Single entry model: RNA polymerases initiate transcription only at the 3 end of the genome,
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
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
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.
Key Terms
B lymphocytes Coiled-coil Dendritic cells Encephalitis Fusion peptide Gangliosides Hemagglutination Hemagglutinin Interferon Nested set Neuraminidase
Pseudotyping Sialic acid Subacute sclerosing
panencephalitis (SSPE) Synctia (singular: syncytium) T lymphocytes Type I integral membrane
protein Type II integral membrane
protein