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Lecture 10

BIOL442 - Lecture 10 - Exit.pdf

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BIOL 442
Christine Dupont

Set 10 Exit Viral egress Assembly exit maturationMost of what is known is based on in vitro studies3D studies using Xray crystallography NMR analysisEx vivo studies involving assembly intermediates of wildtype viruses often suspectTheses are normally only found in low concentration artifactsMore recently genetic mutations knockouts usedAllow intermediates to accumulate at various steps in assembly for analysisPackaging viral genomesHow does viral genome get preferentially packagedIt doesnt in all casesSome strategies to packageeg PicornaviridaeOnlyviral RNA genome is bound by VPg and packaged Why Dont knowMany viral genomes encode packaging signalseg Adenoviridae Herpesviridae Polyomaviridae RetroviridaeThese typically consist of short repeated sequences often associated with promoterenhancer elementsRecognized by viral proteinsPackaging ConstraintsSimplest most obvious problem is constraints imposed by icosahedral capsidsGenerally can only accept 10 variation in lengtheg phage lambda for use as vectorWill accept only inserts between 10 and 20 kpb anything smaller or larger is not efficiently packagedAll DNA viruses except Poxviridae have this constraint strand RNA viruses often have virion size dictated by genome length nucleoprotein coats entire length nondiscriminantly then envelope forms around it this may be the limitation rather than inability to form nucleocapsideg defective interfering particles of RhabdoviridaePackaging viral genomesStrategy of assembly depends largely on capsid structure not type of genome or size2 general mechanisms but not always easy to tell which is being usedSequentialGenome is inserted into performed protien shellSpecialized mechanism to insert or pull in genome is usedeg HerpesviridaeConcerted Protein shell assembles only when associated with genomeeg PicornaviridaeRNA viruses RetroviridaeConcerted AssemblyPoliovirus small capsid selfassembled2 types of particles produced empty capsids and mature virionsPolyproteinP1 P2 P3VP0 VP1 VP3VP2 VP43CD cleaves into peptides VP1 and VP3 with VP2 and 4 still bound by peptide bond5S structural unit5S units can selfassemble into pentamers 5x5S then into capsids wo genomeLast cleavage of VP4 from VP2 only occurs when genome is present this is the concerted contribution New Section 1 Page 1
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