Part 3 of the introduction
Assembly and exit
The structure of a virion determines how it is formed
-> assembly and exit is the final stage of the replication cycle
-> virion requires a built-in switch that can initiate the change stability to instability
-> this trigger can be a binding to a receptor and/or change in concentration of H+ in the endosome
All virions complete a common set of assembly reactions
Virion assembly is dependent on the cellular mechanism
-> nuclear export pathways
-> cellular chaperones
-> cytoplasmid transport systems
-> secretory pathway
Moving cargo around the cytoplasm
Some proteins are made in the cytoplasm, some are made in nucleus and need to be shuttled
back out (nucleopore)
In the cytoplasm there is active transport through the microtubules
viral inclusion bodies = viral components are often visible as factories or inclusions
(formation of virus + replication)
o Concentrates of proteins on internal membranes (polio)
Viral proteins have addresses ensuring correct delivery
NLS: nuclear localization signal
NES: nuclear export signal
Myristoylation : membrane-targeting signal sequences
Membrane-retention signals
Virus assembly is an ordered process
1
, Sequential mechanism: procapsid assembled and subsequently stuffed with viral genome
Concerted mechanism: capsid is constructed around a genome copy
(nucleo)capsid assembly and genome packaging
ss(-)RNA viruses: genome is encapsidated during
replication (influenza: RdRp associated with genome)
complex capsids assemble around scaffolding proteins
which are removed during maturation (herpes, pox,
phages)
Three stages for making sub-assemblies
1. assembly from individual protein molecules
2. assembly from a polyprotein precursor
Polyprotein of 4 viral proteins that interact -> the interaction is closed -> VP4 is removed
3. chaperone assisted assembly: the proteins assamble around the chaperone proteins
Some viruses assemble their capsid in the nucleus
2
Assembly and exit
The structure of a virion determines how it is formed
-> assembly and exit is the final stage of the replication cycle
-> virion requires a built-in switch that can initiate the change stability to instability
-> this trigger can be a binding to a receptor and/or change in concentration of H+ in the endosome
All virions complete a common set of assembly reactions
Virion assembly is dependent on the cellular mechanism
-> nuclear export pathways
-> cellular chaperones
-> cytoplasmid transport systems
-> secretory pathway
Moving cargo around the cytoplasm
Some proteins are made in the cytoplasm, some are made in nucleus and need to be shuttled
back out (nucleopore)
In the cytoplasm there is active transport through the microtubules
viral inclusion bodies = viral components are often visible as factories or inclusions
(formation of virus + replication)
o Concentrates of proteins on internal membranes (polio)
Viral proteins have addresses ensuring correct delivery
NLS: nuclear localization signal
NES: nuclear export signal
Myristoylation : membrane-targeting signal sequences
Membrane-retention signals
Virus assembly is an ordered process
1
, Sequential mechanism: procapsid assembled and subsequently stuffed with viral genome
Concerted mechanism: capsid is constructed around a genome copy
(nucleo)capsid assembly and genome packaging
ss(-)RNA viruses: genome is encapsidated during
replication (influenza: RdRp associated with genome)
complex capsids assemble around scaffolding proteins
which are removed during maturation (herpes, pox,
phages)
Three stages for making sub-assemblies
1. assembly from individual protein molecules
2. assembly from a polyprotein precursor
Polyprotein of 4 viral proteins that interact -> the interaction is closed -> VP4 is removed
3. chaperone assisted assembly: the proteins assamble around the chaperone proteins
Some viruses assemble their capsid in the nucleus
2
