[3] Uncoating

• Reoviruses:

  1. Icosahedral symmetry
  2. Enters via clathrin-pit receptor mediated endocytosis
  3. Outer protein shell protects virus from endosomal degradation
  4. Genome remains inside inner coat
• Adenovirus:

  1. Via penetration by permeabilization of endosome
  2. Adenovirus capsid is partially degraded in acidified endosome
  3. Takes advantage of cellular machinery
  4. Uncoating at nuclear pore
  5. DNA injected across nuclear pore
• Nuclear pore transport is gated, so whatever enters the nucleus needs to be highly regulated
• Materials that can enter the nucleus:

  1. Ribosomal proteins
  2. DNA and RNA polymerases

  Materials that can exit the cell

  1. rRNA complex with the ribosomal proteins
  2. mRNA
  3. other RNA molecules
• Can be taken advantage of for retrograde movement to the nucleus

  Cytoskeletal elements
• Small molecules can diffuse through nuclear pore

  • Larger molecules need to complexed with specific carrier proteins
• For viruses to enter or exit the nucleus, they need to

  1. Mimic carrier proteins
  2. Allow interaction with carrier proteins
• In uncoating, only genetic material enters the cell
• Strategies for Entering Host Nucleus:

  1. Easily diffuse (Parvoviruses)
  2. Shed protein coat outside nucleus
  3. Uncoat in the cytoplasm
  4. Wait for cell division
• Easily diffuse

  • For viruses that are very small

  Shed protein coat

  • Only genome enters

  Uncoat in the cytoplasm

  • Interaction with cellular proteins
  • Carried across nuclear pores

  Wait for cell division

  • For those unable to enter through nuclear pore
  • Nuclear membrane degrades during cell division
• Virus particles do NOT diffuse in cytoplasm

  • Therefore use cell motor machinery
• Viruses and vesicles are large structures, requiring energy to travel through cytosol
• Uncoating locations:

  1. Cell surface
  2. Within cytoplasm
  3. Nuclear pore
  4. Within nucleus
• The general goal of a virus is to produce mRNA
• Catalyzes peptide bond formation

  rRNA peptidyl transferase
• Types of Host-Virus Relationships

  1. Disease and productive infection
  2. Genetic alteration of host cell
• Productive infection means more viruses are produced
• In latent states, no new viruses are produced
• In latent states, viral genomes:

  1. Become part of host cell DNA
  2. Replicates as separate extrachromosomal element
• Host cell becomes a genetic storage for the virus genetic information


  Viral latency
• 2 Replicative Cycles for Bacteriophage Lambda:

  1.  Lytic cycle (productive pathway)
  2. Lysogenic cycle (nonproductive pathway)
• Chromosome with integrated viral NA

  Provirus
• HIV can produce several virions without getting lysed through budding
• Virus that can do productive infection without lysis

  HIV
• Vertebrate viruses can exhibit latency
• Latent form of virus can be:

  1. Provirus- integrated into host genetic material
  2. Episome - when viral genome is maintained as an extrachromosomal circular element
• Provirus - replicates during cell division

  Episomes - can be replicated independently from cell replication
• Virus responsible for chickenpox

  Herpesviridae-3
• When host is immunodeficient, chickenpox can be revived in the form of shingles