Reverse transcriptase is a viral enzyme carried within the capsid of retroviruses, such as HIV, that synthesizes a complementary single-stranded DNA (cDNA) copy using the viral positive single-stranded RNA (+ssRNA) genome as a template.

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HIV or Human Immunodeficiency Virus comprises two strands of RNA, 15 different types of viral proteins, a couple of proteins from the last cell it had infected, and a lipid bilayer membrane. All of these components allow for the cell to infect the immune system and replicate. Each of these components plays a vital role in the spreading of HIV in the body. 

The Structural Biology of HIV

During the replication of animal viruses in eukaryotic host cells, the site of genomic replication depends on the nucleic acid type: most DNA viruses replicate their genomes within the cell nucleus, whereas most RNA viruses replicate within the cytoplasm.

Nucleic acid biosynthesis of Animal Viruses

 Retrieved from https://cdn.rcsb.org/pdb101/learn/resources/structural-biology-of-hiv/index.html#:~:text=HIV (Human Immunodeficiency Virus) is,by a lipid bilayer membrane.


The Structural Biology of HIV Reference

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The genome of HIV consists of two identical strands of RNA. Each strand is around 9700 nucleotides long. The genome contains all of the information that is necessary to synthesize viral proteins.

The Genome of HIV

Capsid Proteins are shaped like cones and they coat the viral RNA. These proteins deliver the RNA around the cell to cause infection. When they come together they form stable hexamers and assemble them to form capsids.

Capsid Proteins Surrounding the Genome

When the virus starts to bud from the surface, proteins will assist in folding. Molecules of cellular transfer RNA will also be captured and initiate the new viral genome in the next cell that is infected.

Cellular Proteins

Integrase will take the viral copy of the infected DNA and will insert it into an infected cellular genome. Integrase allows for the viral DNA genome to remain dormant in cells for decades and it can be difficult to block. Researchers, however, have been able to develop drugs to block this.

Integrase

The trans-activator of transcription will bind to proteins on the viral RNA and act to enhance the amount of proetins that are produced.

Trans-activator of transcription (Tat)

The nucleocapsid protein will attach with viral  RNA and act as a means of protection. This protein protects by ensuring the nucleic acid is protected from digestion by enzymes, allows a spot for a virion to attach (an inactive form of a virus from outside host cell that attaches with the RNA), and allows proteins to penetrate the host cell membrane.

Nucleocapsid Protein (NC)

Viral protein r will guide the viral genome into the genome after infection. This is important for virus replication, stimulates virus transcription, apoptosis, and activation of infected cells. The protein P6 is also involved in the incorporation of Vpr into new viruses.

Viral Protein r (Vpr)

HIV proteases are vital for HIV to continue maturing. The proteins in HIV are called polyproteins. Polyproteins can be cleaved by the HIV protease and allow for HIV to further mature. Proteases are the enzymes that act to increase the breakdown of long chains into smaller ones. 

Proteases

SU and TM are structural proteins that consist of envelope proteins gp120 (envelope glycoprotein) and gp41. These proteins will facilitate HIV's entry into cells. These protein spikes are concentrated with carbohydrates which will ensure that antibodies don't catch them.

SU and TM

Matrix proteins will form a coat on the inside of the membrane and their role occurs when new viruses bud from the infected cells. They are critical for the early stages of the virus ' replication and RNA targeting to the plasma membrane. These proteins are kept in trimers (three molecules or ions of the same substance).

Matrix Protein

The viral infectivity factors will attack one of the cell's defense proteins and destroy them. These are bounded to proteins in the infected cells.

Viral infectivity factor (Vif)

Negative regulatory factors will force the infected cell to stop making several proteins that are important for cell defense. This accessory protein is very important for the progression of HIV.

Negative Regulatory Factor

HIV is a retrovirus which interferes with the body's ability to fight infections. This virus stores its genetic information in RNA instead of DNA.

What type of Virus is HIV?

The science of HIV and AIDS - overview. (2019, October 10). Retrieved from https://www.avert.org/professionals/hiv-science/overview#:~:text=When HIV RNA enters the,proviral DNA inside the cell.


Reference Node HIV/AIDS Infection

Reverse Transcriptase (Viral Enzyme)

While most DNA viruses replicate inside the host cell's nucleus, large DNA viruses, such as poxviruses, are exceptions that replicate within the cytoplasm.

Cytoplasmic Replication of DNA Viruses

While RNA viruses that infect animal cells generally replicate in the cytoplasm, the influenza virus is a notable exception to this replication location.

Exception to RNA Animal Virus Replication Location

An RNA-dependent RNA polymerase (RdRP) is a viral enzyme that synthesizes a complementary RNA strand from an RNA template, enabling the replication and transcription of viral RNA genomes.

RNA-dependent RNA Polymerase

If an animal virus has a positive single-stranded RNA (+ssRNA) genome, its genomic RNA acts similarly to cellular mRNA and can be translated directly by host ribosomes to synthesize viral proteins.

Replication of +ssRNA Animal Viruses

If an animal virus has a single-stranded DNA (ssDNA) genome, host enzymes synthesize a complementary second strand to produce double-stranded DNA (dsDNA). This double-stranded DNA is then replicated, transcribed, and translated in the same manner as host cell DNA.

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