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Target site recognition by a diversity-generating retroelement.

Huatao Guo1, Longping V Tse, Angela W Nieh

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Area of Science:

  • Molecular Biology
  • Genetics
  • Bioinformatics

Background:

  • Diversity-generating retroelements (DGRs) are mobile genetic elements that introduce genetic diversity into host genomes.
  • DGRs utilize a unique retrotransposition mechanism to diversify protein-encoding DNA sequences.
  • The Bordetella bacteriophage BPP-1 DGR serves as a model for studying DGR mechanisms.

Purpose of the Study:

  • To elucidate the target site requirements for efficient retrohoming of the BPP-1 DGR.
  • To investigate the role of specific DNA structures downstream of the variable repeat (VR) in DGR function.
  • To assess the potential of DGRs as tools for directed protein evolution.

Main Methods:

  • Site-directed mutagenesis of the DGR target site.
  • Structure-specific nuclease digestion to confirm DNA secondary structures.
  • Marker coconversion assays to evaluate retrohoming efficiency and integration site.
  • Transplantation of DGR components into a heterologous gene system.

Main Results:

  • A 24 bp sequence downstream of the VR, forming a hairpin/cruciform structure, is essential for efficient DGR retrohoming.
  • The hairpin/cruciform structure's stem sequence is variable, but its integrity is critical; the loop has sequence-dependent functions.
  • Transplantation of the DGR machinery and the hairpin/cruciform region successfully targeted a heterologous gene for diversification.

Conclusions:

  • The conserved hairpin/cruciform structure downstream of the VR is a key determinant of DGR target site function.
  • DGRs influence retrohoming efficiency but not the site of cDNA integration.
  • DGRs represent promising tools for in vivo DNA diversification and directed protein evolution.