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Retroviruses

Retroviruses. By: 10/06/GS/2981 10/06/PS/3223 10/06/PS/3189 10/06/GS/2999 10/06/GS/2991. Introduction. A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome.

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Retroviruses

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  1. Retroviruses By: 10/06/GS/2981 10/06/PS/3223 10/06/PS/3189 10/06/GS/2999 10/06/GS/2991

  2. Introduction • A retrovirus is an RNA virus that is duplicated in a host cell using the reverse transcriptase enzyme to produce DNA from its RNA genome. • The DNA is then incorporated into the host's genome by an integrase enzyme. • The virus thereafter replicates as part of the host cell's DNA. Retroviruses are enveloped viruses that belong to the viral family Retroviridae.

  3. Intro ctn… • A special variant of retroviruses are endogenous retroviruses which are integrated into the genome of the host and inherited across generations. • In most viruses, DNA is transcribed into RNA, and then RNA is translated into protein. • The order of steps from a retroviral gene to a retroviral protein is: RNA → DNA → RNA → protein.

  4. Genes Retrovirus genomes commonly contain these three open reading frames that encode for proteins that can be found in the mature virus: • group-specific antigen (gag) codes for core and structural proteins of the virus; • polymerase (pol) codes for reverse transcriptase, protease and integrase; and, • envelope (env) codes for the retroviral coat proteins.

  5. structure • Virion (a complete viral particle) of retroviruses consist of enveloped particles about 100 nm in diameter. • The virions also contain two identical single-stranded RNA molecules 7-10 kilobases (kb) in length. • Although virions of different retroviruses do not have the same morphology or biology, all the virion components are very similar.

  6. Main virion components • Envelope: composed of lipids obtained from the host plasma membrane during budding process as well as glycoproteins encoded by the env gene. • RNA: consists of a dimer RNA. • Proteins: consisted of gag proteins, protease (PR), pol proteins and env proteins.

  7. Gag proteins are major components of the viral capsid. • Protease is expressed differently in different viruses. It functions in proteolytic cleavages during virion maturation to make mature gag and pol proteins. • Pol proteins are responsible for synthesis of viral DNA and integration into host DNA after infection. • Finally, env proteins play role in association and entry of virion into the host cell.

  8. classification • Oncoviruses Human T lymphocytes Viruses • HTLV1 • HTLV2 Both associated with malignancies (leukemia and other tumors)

  9. lentiviruses Human Immunodeficiency Virus. • HIV1 • HIV2 Which cause acquired immunodeficiency syndrome (AIDS) • spumaviruses

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