Lecture 6: Herpesvirus

Question 1

general patterns of infection

Answer 1

Acute: rhinovirus, rotavirus, influenza
latent- systematic and asymptomatic: herpes simplex
persistent- asymptomatic(leads to death): JC virus
persistent- pathogenic (asymptomatic): HIV, measles

Question 2

all infections start at

Answer 2

acute phase

Question 3

general properties of latent infections

Answer 3

• viral gene products that promote productive replication are not made/ found in low [ ]
• cells harboring latent viral genome are poorly recognized by immune system
• viral genome persists intact so productive infection can be initiated to spread infection to new hosts

Question 4

capsid= 125nm; virion= 200 nm
enveloped: yes
capsid: icosahedral (T=16)
baltimore class 1
linear, dsDNA, repeat sequence
segments:  1
genes: ~90 proteins
genome size: 125-250 kb
unique traits: latents infections, alter host defense, nuclear budding

Answer 4

herpesvirus

human herpesviruses (HSV-1 to 8)

Question 5

describe herpes virion structure

Answer 5

• envelope- lg and baggy, >10 glycoproteins
• capsid- icosahedral (T=16)
• tegument (proteins stuffed in space) - viral proteins and mRNA, >15 proteins, promote early infection
• dsDNA genome- circular but packaged linear, infectious

Question 6

describe herpes receptor binding to cell

Answer 6

complex process involving multiple ligands and host cell receptors

initial binding to primary cell receptor

• heparan sulfate proteoglycan (cell)
• virus nonspecific
• gB and gC ligand (virus)

Question 7

describe herpes membrane fusion

Answer 7

viral gD ligand binds to virus specific co-receptors

• herpesvirus entry mediator (HSEM): lymphoid cells
• nectin 1 and 2: skins, brain, spinal ganglia

binding of co-receptor triggers viral envelope fusion with cell membranes

• requires several viral surface proteins (gB, gH, gL)
• fusion may occur at pm or endosome (target cell specific)

Question 8

HSV-1 genetic map interpretation

Answer 8

linear

unique structures

• two covalently-linked components: Long (U) and Short (S)
• terminal and internal inverted repeats

recombination common
-four genome isomers and all are infectious

Question 9

herpesvirus gene: promoter ratio

Answer 9

1:1

Question 10

genes that are transcription activators

first few hours

Answer 10

immediate-early (alpha) genes

Question 11

genes for replication of viral DNA

4-8 hours

Answer 11

early (beta) genes

Question 12

genes for structural and regulatory proteins
major group
regulatory proteins; control most defenses

Answer 12

late (gamma) genes

Question 13

describe HSV-1 transcription (early)

Answer 13

role of tegument proteins released into nucleus w/ viral genome

• VP16- transcription activator of viral genes and recruits cellular transcription factors
  - must be present to become viral

-Vhs (virion host shutoff)- interacts w/ cell proteins to degrade mRNAs; vial mRNA accumulates faster

Question 14

will block VP16 is expressed too much

Answer 14

ICP4