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<p>Insertion sequences (IS) are key players in bacterial genome plasticity and horizontal gene transfer. IS<i>91</i> family members, belonging to the HUH superfamily of single-strand nucleases, are often linked with antibiotic resistance genes. Among these, the element IS<i>91</i> is unique as it also carries a sequence called <i>orf121</i>, whose stop codon overlaps with the start codon of <i>tnpA</i>, a highly conserved feature of IS<i>91</i> isoforms. We show that Orf121 serves as a dual regulator of IS<i>91</i> transposition: Orf121 inhibits transposition activity of TnpA while facilitating accurate excision of IS<i>91</i> single-strand circular intermediates. This accurate excision reduces one-ended transposition events, i.e., events arising when proper termination fails, leading to the co-mobilization of adjacent DNA. We also provide evidence that the bottom-stranded ssDNA circular intermediate is the functional substrate IS<i>91</i>. These findings highlight a sophisticated regulatory strategy balancing IS<i>91</i> mobility and genetic stability.</p>

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Dual regulatory role of IS91-encoded Orf121 in IS91 transposition

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月25日

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  • Aurélien Fauconnier,
  • Sandra Da Re,
  • Margaux Gaschet,
  • Thomas Jové,
  • Marie-Cécile Ploy,
  • Cécile Pasternak

摘要

Insertion sequences (IS) are key players in bacterial genome plasticity and horizontal gene transfer. IS91 family members, belonging to the HUH superfamily of single-strand nucleases, are often linked with antibiotic resistance genes. Among these, the element IS91 is unique as it also carries a sequence called orf121, whose stop codon overlaps with the start codon of tnpA, a highly conserved feature of IS91 isoforms. We show that Orf121 serves as a dual regulator of IS91 transposition: Orf121 inhibits transposition activity of TnpA while facilitating accurate excision of IS91 single-strand circular intermediates. This accurate excision reduces one-ended transposition events, i.e., events arising when proper termination fails, leading to the co-mobilization of adjacent DNA. We also provide evidence that the bottom-stranded ssDNA circular intermediate is the functional substrate IS91. These findings highlight a sophisticated regulatory strategy balancing IS91 mobility and genetic stability.