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Effect of polypurine tract (PPT) mutations on human immunodeficiency virus type 1 replication: a virus with a

Lesa R Miles1, Beth E Agresta, Mahfuz B Khan

  • 1Department of Microbiology, Biochemistry and Immunology, Morehouse School of Medicine, 720 Westview Dr. S. W., Atlanta, GA 30310, USA.

Journal of Virology
|May 14, 2005
PubMed

Insights

Polypurine tract (PPT) mutations impact viral replication. Disrupting the 3' end of the PPT sequence significantly reduces infectivity, yet a randomized PPT retains some function, confirming its importance in viral replication.

Area of Science:

  • Virology
  • Molecular Biology
  • Genetics

Background:

  • The polypurine tract (PPT) is a crucial sequence in retroviral replication, essential for initiating DNA synthesis.
  • Previous in vitro studies suggested the importance of the PPT sequence, but its role in infectivity and replication competence required further investigation.

Purpose of the Study:

  • To investigate the impact of polypurine tract (PPT) mutations on viral infectivity and replication.
  • To determine the specific roles of the 5' and 3' ends of the PPT sequence in viral replication.
  • To assess the replication capacity of a virus with a randomized or absent PPT sequence.

Main Methods:

  • Introduction of PPT mutations into the viral clone NL4-3KFSdelta nef.
  • Assessment of single-round infectivity and virion production.
  • Analysis of two-long terminal repeat (2-LTR) circle formation using junction analysis and real-time PCR.
  • Introduction of the PPTSUB mutation into a replication-competent virus to evaluate progeny virion replication.

Main Results:

  • All PPT mutations affected viral replication, with 3' end mutations showing a greater impact on infectivity than 5' end mutations.
  • A randomized PPT sequence (PPTSUB) retained 12% of wild-type (WT) infectivity and produced viral particles.
  • PPTSUB infection led to a 3.5-log increase in 2-LTR circles compared to WT.
  • The PPTSUB mutant replicated in a replication-competent virus, with infectivity increasing upon passage and reverting to WT PPT sequence.

Conclusions:

  • The 3' end of the PPT is critical for plus-strand DNA priming during retroviral replication.
  • A virus lacking a functional PPT can still replicate, albeit at a low level.
  • Viral sequences can rapidly revert to a functional PPT, highlighting its essential role in maintaining viral fitness.

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