Section 6.1 Flashcards
Animal Virus Genome:
DNA (mostly ds)
The larger the DNA genome, the greater _________ from Cellular Machinery
Independence
Cytoplasmic-replicating DNA viruses encode their own:
DNA polymerase AND RNA polymerase
Nuclear-replicating DNA viruses encode their own:
DNA polymerase
but use host cell’s RNApol
1) Herpersviridae: frequently show _____-_______ ________ and is never cleared from the body
life-long persistence
a herpesviridae viruses infect ___
nervous system (neurotropic)
B and Y herpesviridae viruses infect ___
lymphatic system (lymphotropic)
Examples of herpesviridae:
EBV (Epstein-Barr virus), HSV-1, HSV-2, Chicken pox (varicella zoster virus VZV)
facts about EBV
- originally discovered un human tumor cells
- 95% of adults carry it from early life infection
- initial infection can be either asymptomatic or cause mononucleosis
- replicates in mucosal cells “kissing disease” and becomes latent in B cells
Structure of herpesviridae:
- icosohedral nuclear capsid (made of 6 proteins)
- wrapped in envelope
- envelope covered with 10< glycoproteins
- matrix (tegument) : large space between envelope and capsid made up of 15-20 proteins
matrix (tegument) is a :
large space between envelope and capsid made up of 15-20 proteins
Function of matrix: (2 things)
1) structural support (maintains structure of virion)
2) released after infection in host cell to do stuff
What do Herpesviruses first do?
1) initiate a primary productive infection by
- replicating its DNA
- forming viral particles
- killing host cell
- release progeny viruses
initial symptoms of oral sores, genital sores or chicken pox
After Herpesviruses productive infection:
- immune response limits viral replication
- viral DNA enters LATENT state
then two options:
1) remain without symptoms, no infectious virus is detectable in latent phase
2) reactivation of latent virus can lead to another productive infection
Herpes Simple Virus (HSV) genome:
- linear dsDNA —–> circulaires in latency
- 3 repeated sequences and 2 unique regions
-ends have packaging signals (from concatamer made in replication)
Steps of entry of HSV:
- HSV glycoproteins: attachment and fusion with cell membrane
- capsid and matrix proteins: release into cytoplasm
-nucleocapsid: goes to nucleus of cell with the help of host microtubule cytoskeleton
- capsid: docks at nuclear pore complex
—–> viral DNA released into nucleus and capsid remains in cytoplasm
HSV gene expression stages (3 gene classes)
1- immediate early genes (5 genes)
2- early genes
3- late genes
HSV gene expression STAGE 1 immediate early genes
transcription
VF16 (aka aTIF) needs to go into the nucleus for transcription to occur
HSV gene expression STAGE 2
Early genes:
Activated by the products of the IE genes
- encode DNA replication functions
HSV gene expression STAGE 3
Late genes:
structure and egress expression starts after DNA replication has begun
HSV replicates its DNA using: ___ _____ _______ method
RCR: rolling circle replication
How does RCR work
- it generates a continus strand of concatameric viral DNA
- this concatameric DNA is the substrate for encapsidation
- cleavage encapsidation protons recognize the a sequences (later becomes the ends) and puts everything else in between
Final packaged DNA by RCR is called a ________
procapsid
HSV replicates in ______ ________
replication factories
in HSV replication factory:
Viral DNA replicates
late genes get expressed
> 30 genes assemble the vision
mature HSV capsid leaves nucleus through _____ ______
therefore undergoing:
double nuclear membrane
1- primary envelopment: to acquire mature envelop structure
2- secondary envelopment: in a secretory vesicle that then fuses with plasma membrane to release virion from cell
herpesviruses get their envelopes from ________ ___ _______
Inside the cell
NOT BY BUDDING OUT THE CM
productive infection of HSV-1 happens in __ __________ where new visions are produced
lip epidermis (hence cold sores)
HSV-1 latent infection
HSV-1 is neurotropic: enters a sensory neuron at infection site
capsid migrates within neuron and enters nucleus but cannot be productive
——-> cuz no cellular protiens in neuron’s for IE genes
During latent infection period of HSV-1
DNA present as histone wrapped mini chromosome
—-> transcription is therefore repressed and no DNA can replicate
Only reactivated by stress or other stimulus, leading to infectious visions reproduced and going to epidermal lip tissue
