Presentation on theme: "Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae"— Presentation transcript:
1Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae VirionGenomeGenes and proteinsViruses and hostsDiseasesDistinctive characteristics
2Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae VirionParamyxoviruses: spherical, diameter 150–300 nm, also found as filaments.Rhabdoviruses: bullet-shaped rods, nm.Envelope derived from plasma membrane.Coiled helical nucleocapsid.
3Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae GenomeLinear ssRNA, negative sense.Single segment.Paramyxoviruses: 15–18 Kb.Rhabdoviruses: 11–12 Kb.
4Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae Genes and proteinsFive 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,
6Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae DiseasesParamyxoviruses: 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 virusin cattle. Numerous insect and plant diseases.
7Paramyxoviruses and Rhabdoviruses Paramyxoviridae and Rhabdoviridae Distinctive characteristicsRNA-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).
8VirionThe mononegaviruses: a group of related negative-strand RNA virusesSingle RNA genome packaged in a helical nucleocapsidEnvelope derived from host plasma membraneViral RNA polymerase packaged in the virionmRNAs made by a start-stop mechanism
9Virion Rabies is a fatal human encephalitis caused by a rhabdovirus Infect wide variety of hostsRabies virus is of significant concern to human healthInfected by virus-containing saliva from bites of infected animalsInfection results in a fatal encephalitisMeasles is a serious childhood disease caused by a paramyxovirus
10VirionParamyxovirus and rhabdovirus virions have distinct morphologiesStructure of paramyxoviruses
11VirionParamyxovirus and rhabdovirus virions have distinct morphologiesStructure of rhabdoviruses
12VirionViral envelope proteins are responsible for receptor binding and fusion with cellular membranesFig Schematic diagram of paramyxovirus virion.
14Genome Genome RNA is contained within helical nucleocapsids Structure of paramyxovirus helical nucleocapsid
15GenomeParamyxoviruses enter the cell by fusion with the plasma membrane at neutral pHBindingSendai : HN - sialic acidMeasles : H - CD46, CD150/SLAMUpon binding, F protein undergoes conformational change that allows insertion of fusion peptide to plasma membrane.
16GenomeGene order is conserved among different paramyxoviruses and rhabdovirusesLeader regionSignals for initiation of RNA synthesisSignals for packaging of full-length RNA genomeNo cap, no poly A tailIntergenic sequenceControls txn termination, polyadenylation, reinitiationFig Paramyxovirus genome RNA.
17Genes and ProteinsViral messenger RNAs are synthesized by an RNA polymerase packaged in the virionViral RNA polymerase initiates transcription exclusively at the 3’ end of the viral genome
18Genes and Proteins(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,Fig Alternative models for transcription of mononegavirus genome RNA.
19Genes and ProteinsThe promoter for plus-strand RNA synthesis consists of two sequence elements separated by one turn of the ribonucleoprotein helixmRNAs are synthesized sequentially from the 3 to the 5 end of the genome RNA
20Genes and ProteinsFig Paramyxovirus transcription and replication.
21Genes and proteinsThe 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.
22Genes and proteins Functions of P, C, and V proteins P : cofactor required for viral RNA synthesisdirects binding of L to the promoterV : not normally required for replicationinterferes with host mechanisms that reduceviral replicationC : required for formation of infectious virionexact roles not understood
23Genes and proteinsN protein levels control the switch from transcription to genome replicationVirions are assembled at the plasma membraneEnvelope protein inserted into plasma membraneMatrix protein associates with cytoplasmic face of p.m.Nucleocapsid interact w/ matrix proteinVirions are made by budding from p.m.