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Retroviruses and retrotransposons both insert copies of their genetic elements into the genome of the host cell. Thus, the viral genes are passed on when the host genome is replicated or translated. A typical retroviral DNA sequence contains 3-4 genes that encode the different proteins required for its structural assembly and function as a molecular parasite. This DNA is transcribed into a single mRNA, which is very similar in structure to conventional mRNAs, i.e., it is capped at the 5’...
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Retroviruses have a single-stranded RNA genome that undergoes a special form of replication. Once the retrovirus has entered the host cell, an enzyme called reverse transcriptase synthesizes double-stranded DNA from the retroviral RNA genome. This DNA copy of the genome is then integrated into the host’s genome inside the nucleus via an enzyme called integrase. Consequently, the retroviral genome is transcribed into RNA whenever the host’s genome is transcribed, allowing the...
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As the name suggests, non-LTR retrotransposons lack the long terminal repeats characteristic of the LTR retrotransposons. Additionally, both LTR and non-LTR retrotransposons use distinct mechanisms of mobilization. Non-LTR retrotransposons are further divided into two classes - Long interspersed nuclear elements (LINEs) and short interspersed nuclear elements (SINEs), both of which occur abundantly in most mammals, including humans. Some of the active non-LTR retrotransposons in humans are L1...
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Link between primate lentiviral coreceptor usage and Nef function.

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Simian immunodeficiency virus (SIVsmm) can switch coreceptor usage, leading to CD4(+) T cell depletion. Mutations in the Nef protein explain this switch by altering interactions with the CD3 zeta chain.

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Area of Science:

  • Virology
  • Immunology
  • Molecular Biology

Background:

  • Simian immunodeficiency virus (SIVsmm) infection in sooty mangabeys typically maintains CD4(+) T cell counts despite high viral loads.
  • Rare SIVsmm strains gain CXCR4 coreceptor tropism, causing CD4(+) T cell depletion without overt immunodeficiency.

Purpose of the Study:

  • To investigate the molecular mechanisms behind SIVsmm's switch to CXCR4 tropism and subsequent CD4(+) T cell depletion.
  • To understand the role of Nef protein mutations in this tropism shift and its impact on T cell interactions.

Main Methods:

  • Analysis of SIVsmm strains with differing coreceptor tropisms.
  • Investigation of Nef protein mutations and their effects on TCR-CD3 complex interaction.
  • Comparative analysis of viral replication in different T cell subsets (CCR5+ memory vs. CXCR4+ naive).

Main Results:

  • CXCR4-tropic SIVsmm strains evolved specific Nef mutations (I132V, I123L, L146F).
  • These Nef mutations disrupt the interaction with the CD3 zeta chain, impairing TCR-CD3 downmodulation.
  • CD3 downmodulation appears advantageous for replication in activated CCR5(+) memory T cells but not resting CXCR4(+) naive T cells.

Conclusions:

  • Nef-mediated CD3 downmodulation is a key factor influencing SIV tropism and pathogenesis.
  • The loss of CD3 downmodulation function in CXCR4-tropic SIVsmm explains its distinct replication profile.
  • This finding provides insight into why HIV-1, often lacking CD3 downmodulation, frequently uses CXCR4, unlike most SIVs.