Herpes Simplex Virus

Question 1

Stages

Answer 1

Attachment
Penetration and Uncoating
Immediate Early Gene Expression
Early Gene Expression
Genome Replication
Late Gene Expression
Assembly
Release

Question 2

Attachment

Answer 2

• receptor mediated attachment
• heparan sulfate proteoglycans
• multiple receptors may be used due to multiple spikes

Question 3

Penetration and Uncoating

Answer 3

• direct fusion between the plasma membrane and viral envelope triggered by the binding to the receptor
• dispersal of tegument
• docking of nucleocapsids into nuclear pore complex and injection of viral DNA into nucleus

Question 4

Immediate Early Gene Expression

Answer 4

• alpha-TIF turns on the expression of the 5 alpha genes, which then code for a different transcription factor
• alpha gene mRNAs are exported to the cytoplasm for translation
• alpha proteins are then imported into the nucleus, which activates transcription of viral beta and gamma genes and represses alpha transcription

Question 5

Early Gene Expression

Answer 5

• beta genes transcribed only in the presence of alpha proteins
• the beta gene mRNAs are then exported to the cytoplasm for translation
• the beta gene proteins are then imported into the nucleus for genome replication and some aren’t imported
• the beta proteins activate gamma gene transcription directly and indirectly

Question 6

Genome Replication

Answer 6

• the virus codes for everything that it needs for replication through beta gene products
• genome replication by rolling circle replication
• replication initiated at defined origins, replication fork only needs to be assembled once
• rolling circle mechanism generates head to tail concatameres

Question 7

Late Gene Expression

Answer 7

• gamma proteins repress transcription of alpha and beta genes
• gamma genes encode virion structural proteins. nucleocapsid protein imported into nucleus
• alpha-TIF and other tegument proteins retained in cytoplasm
• enveloped spike proteins inserted in RER; most traffic to Golgi, some traffic to inner nuclear membrane

Question 8

Assembly

Answer 8

• nucleocapsid assembly occurs in nucleus and ends with mature visions budded into lumen space of trans-Golgi
• formation of empty nucleocapsid shell (begins with portal, scaffolding proteins to support, and nucleocapsid proteins added to build shell)
• shell-stuffing puts viral DNA into nucleocapsid
• primary envelopment of nucleocapsids at inner nuclear membrane and exit into cytoplasm
• binding of tegument (tegumentation
• secondary envelopment as tegumented nucleocapsids bud into lumen of trans-Golgi vesicles to form mature, enveloped virions with spike

Question 9

Release

Answer 9

• can occur through two mechanisms
  
  • cell lysis
  • exocytosis - happens before cell lysis, exocytic vesicles can traffic to plasma membrane and fuse with it, releasing mature, enveloped virions.