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What is the Herpes Simplex Virus?
The herpes simplex virus (HSV) is part of the Herpesviridae family, which is a group of viruses that feature a double stranded DNA genome, icosahedral capsid, tegument, and an envelope embedded with glycoproteins. There are two types of HSV: HSV-1 and HSV-2. HSV-1 causes oral sores, while HSV-2 is responsible for genital herpes. The virus can remain dormant in nerve cells for a long period of time before an outbreak occurs. Generally, replication of herpes simplex virus involves the invasion of a host cell, entry into its nucleus, replication of viral DNA, assembly of viral components, and budding out of the cell.
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The Herpes Simplex Virus Enters the Host Cell
Replication of the herpes simplex virus begins by docking with a host cell. The virus utilizes its glycoproteins to recognize the surface proteins of the host cell. When the two come into contact, the viral envelope fuses with the plasma membrane of the host cell. As this happens, the capsid within the viral envelope travels through the opening in the plasma membrane and enters the host cell's cytoplasm. The capsid contains the genetic material of the virus. The capsid is surrounded by a layer of proteins called the viral matrix or tegument.
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The Herpes Simplex Virus Enters the Host Cell Nucleus
Once the capsid is in the cytoplasm, it travels toward the nucleus. It utilizes the cell's scaffolding, including the microtubules, to move from the plasma membrane to the nucleus. At the nucleus, the capsid binds to the nuclear pore and releases the viral genetic material. It then travels into the nucleus, where it replicates.
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DNA Replication and Viral Assembly
In the nucleus, the double stranded DNA of the herpes simplex virus circularizes. The host's transcription enzymes produce mRNA that codes for viral proteins necessary for DNA replication and for the construction of new capsids. The mRNA leaves the nucleus and heads towards the ribosomes. The viral proteins return to the nucleus. Some replicate the DNA, while others form into capsids.
After replication, the copied DNA is surrounded by the capsid. The host cell's nuclear envelop becomes embedded with viral proteins. The capsid buds through the inner nuclear envelope and gains a temporary membrane that fuses with the outer nuclear envelope.
Upon exiting the nucleus, the capsid travels through the cytoplasm until it buds through a golgi vesicle. The golgi is lined with viral matrix proteins, which will surround the capsid. As it continues through the golgi, the virus gains an envelope embedded with glycoprotein spikes.
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Exiting the Host Cell
After the virus is assembled, it is deposited near the plasma membrane. Then, the virus fuses with the plasma membrane and exits the cell. It will invade a nearby cell to replicate.
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1. "Herpes Virus Replication or Life Cycle." Russell Kightley Media. http://www.rkm.com.au/VIRUS/HERPES/herpes-replication.html
2. "Replication of Herpes Simplex Virus." Microbial Life. http://www.sumanasinc.com/webcontent/animations/content/herpessimplex.html