Flashcards in Cytomegalovirus, EBV, Kaposi's Sarcoma- Associated Herpesvirus Deck (53)
T or F. CMV, EBV, and KSHV (HHV8) are all herpes viruses
All share a tropism for what?
Which of the three are oncogenic viruses?
EBV and KSHV
Describe the structure of herpesviruses.
-icosahedral capsid surround by a lipid envelope containing ~12 virally derived glycoproteins
tegumnet- has important proteins for replication
Describe the genome of herpesvirus.
large, linear, double-stranded DNA ca. 150-250 kilobase pairs
CMV is largest
How do herpesviruses replicate?
genome is replicated and viruses assembled in the nucleus
T or F. In general, herpesviruses produce self-limiting infections in which the primary infection is often asymptomatic.
However, life-threatening infections or cancers can occur, especially in immune compromised hosts (neonates, AIDS, etc.)
Is the replicative cycle of herpesviruses lytic or lysogenic?
lytic in a variety of cell types
Following virus attachment, how does viral penetration occur?
by virus glycoprotein- mediated fusion of envelope and plasma membrane (pH independent)
What does the released nucleocapsid do after entering the cell?
migrates to nuclear envelope via microtubules, uncoats, and DNA enters the nucleus. Virion components act to shut off host macromolecular synthesis
Then what happens?
Programmed expression of viral genes- cascade regulation
What is the order of proteins transcribed in these viruses?
- immediate early genes
- early genes
- late genes
What do immediate early (IE) genes encode?
virus-specific transcription factors
i. use host RNA polymerase II
ii. stimulate transcription at virus early promoters
What do early genes encode?
many nonstructural proteins, enzymes
Specifically, what kinds of proteins/enzymes do early genes encode?
-DNA replication machinery, including viral DNA polymerase
-thymidine kinase (tk) which phosphorylates a variety of nucleotides besides thymidine
What do late genes encode?
structural proteins (capsids, glycoproteins)
What is late gene transcription dependent on?
IE transcription factors and genome replication
Where does virus assembly occur?
nucleus- where nucleocapsids bud first into the perinuclear space
What happens after viral assembly?
virus particles migrate to the cell surface where they are released
What is latency?
situation in which entire genomes are maintained extrachromosomally in the host indefinitely, but no virus are produced
What are the stages of latency?
When does reactivation generally occur?
when there is a lapse in immunity and results in the production of virus particles and recurrent infection
How many herpesviruses are there?
8- classified on basis of their genome arrangement and latency tropism
neurotropic for latency,
aggressive lytic growth
What are some types of alphaherpesviruses?
a.Herpes simplex virus (HSV)-1
c.Varicella-zoster virus (VZV)
lymphotropic for latency,
What are some types of betaherpesviruses?
b.Human herpesvirus-6 (HHV-6)
lymphotropic for latency,
What are some types of gammaherpesviruses?
HHV-8 (Kaposi's sarcoma)