week 4 Flashcards
genome packaging (adeno)
discrimination between viral and cellular rna/dna is due to packaging signals in the viral genome. adenovirus packaging signal is near left inverted repeat and consists of a set of repeated sequences overlapping with enhancers that stimulate late gene transcription
genome packaging: herpesvirus
herpes replication produces multiple genomes joined together called concatemers. have packaging signals pac1 and pac2 on both sides of the genome that is recognized and cleaved within the repeat DR1
genome packaging HIV
packaging signal is in spliced regions to ensure that no mRNA is packaged into virions.
how are the structural units assembled?
- by association of individual monomeric proteins that are translated as separate components
- from large polyprotein subunits that are refolded after proteolytic processing
- with the assistance of viral or cellular chaperones that facilitate correct folding of the strucural proteins
- using viral scaffhold proteins, they are not part of the mature virus but used to assemble to bring components together
assebly of dna viruses
usually assemble in the nucleus. they are usually released from the cell after breakdown of the cell due to toxic viral proteins. the structural proteins are often transported into the nucleus.
nuclear localisation signals
viral proteins often contain a sequence known as nuclear localization signal that binds to nuclear transport proteins. the signal usually has a high ocntent of basic amino acids. directs proteins to the nucleus, often used by dna viruses
herpesvirus assembly and maturation
assemble its capsid in the nucleus. then takes envelope from nucleus and is transported through the er and buds of to reach golgi where the final assembly and aquiring of envelope occurs. exits via exocytosis
assembly of influenza virus
the 8 genomic segments are replicated in the nucleus but assembly happens at the plasma membrane. switch to produce genome instead of mRNA causes accumilation fo genome
RNA interactions between the 8 segments and packaged in virion
assembly of enveloped viruses
the envelope comes from the cell membrane when thevirus exits via exocytosis. uses some different strategies:
- envelope glycoproteins and capsid are needed for budding (alphaviruses)
- internal matrix or capsid proteins drive budding (retroviruses)
- envelope proteins drive budding (corona)
- matrix proteins drive budding but additional components are needed
flaviviris maturation and exit
assembles in the lumen of the rough er and is transported out of the cell via thhe secretory pathway and released via exocytosis. pH and cellular proteins contribute to the maturation of the virion. host enzyme furin cleaves pre-M (envelope protein?) to M, before being cleaved it prevents fusion of envelope with celllular membranes
HIV assembly, maturation and exit
envelope protein is cleaved by the cellular protease furin which releases the transmembrane and surface unit of envelope precursor. env is extensively modified in the er golgi network. the gag proteins are also modified. HIv assembles as the plasma membrane by accumulation of envelope proteins in the plasma membrane
vaccinia virus exit
uses 2 different components of the cytoskeleton
- micotubules to move from replication sites to the cell periphery
- actin to exit
exit of non-enveloped viruses
non enveloped viruses often exit through cell lysis. many enteric non-enveloped viruses use a different strategy that involves enrobing themselves in a lipid envelope during exit. some viruses use apoptosis and then exits in apoptotic bodies. both of these protects against antibody detection since they are concealed.
