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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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Intraluminal vesicles (ILVs) are small vesicles 50-80 nm in diameter formed during the maturation of early endosomes. A specialized endosome containing numerous ILVs is called a multivesicular body (MVB). ILVs contain internalized molecules such as antigens, nucleic acids, proteins, and metabolites. Some of these molecules are released from the MVBs inside exosomes and are transported to other cells. Other MVBs contain molecules that are retained in the ILVs and are later degraded within the...
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Assembly and Purification of Prototype Foamy Virus Intasomes
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Retroviral intasomes arising.

Alan N Engelman1, Peter Cherepanov2

  • 1Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Medicine, Harvard Medical School, Boston, MA 02115, USA.

Current Opinion in Structural Biology
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Summary
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Retroviral DNA integration involves varying numbers of integrase proteins, challenging the long-held belief that a tetramer is universally required. New structures reveal diverse intasome architectures across different retroviral species.

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Area of Science:

  • Molecular Biology
  • Structural Biology
  • Virology

Background:

  • Retroviral DNA integration is mediated by the intasome nucleoprotein complex.
  • Previously, functional spumaviral intasomes were known to contain an integrase homotetramer, leading to the assumption of universal tetrameric catalysis.
  • This assumption has been challenged by recent structural findings.

Purpose of the Study:

  • To describe alternative intasome architectures revealed by new structures from four different retroviruses.
  • To highlight evolutionary and structural constraints influencing integrase-DNA stoichiometry.
  • To present a revised understanding of intasome composition across Retroviridae.

Main Methods:

  • X-ray crystallography was used to determine the structures of intasome complexes.
  • Comparative analysis of newly elucidated structures from diverse retroviral species.
  • Examination of evolutionary and structural factors influencing protein-DNA complex formation.

Main Results:

  • The number of integrase subunits in the intasome core structure varies significantly between retroviral groups.
  • Spumaviruses utilize four integrase subunits, while alpha- and beta-retroviruses require eight.
  • Lentiviruses employ up to sixteen integrase subunits in their intasome complexes.

Conclusions:

  • Intasome architecture is not conserved across all retroviruses, with varying integrase stoichiometries.
  • Structural and evolutionary pressures dictate the diverse number of integrase molecules per intasome.
  • This diversity impacts the mechanism and regulation of retroviral DNA integration.