{
  "abstract": "Prokaryotic transcription factors (TFs) lie at the core of antimicrobial resistance, controlling genes that let bacteria survive antibiotic exposure. The AraC/XylS family of TFs is defined by a ~99-residue DNA-binding domain composed of two helix-turn-helix (HTH) motifs. While this two-motif architecture is considered the minimal functional unit, the striking sequence and structural similarity between both HTH motifs raises the question of whether it evolved from a single ancestral HTH domain. Here, we designed two C-terminal truncations of MarA, comprising a single HTH motif, differing by seven-residues (IRSRKMT). Electrophoretic-mobility shift assays reveal that both constructs specifically bind the marbox sequence as reconstituted dimers, while size-exclusion chromatography shows they exist in a monomer-dimer equilibrium in solution. Despite retaining DNA-binding capacity, the truncations diverge functionally: while MarA64 (including IRSRKMT) activates transcription and confers regular erythromycin tolerance, MarA57 (lacking IRSRKMT) yields a transcriptionally inactive complex that suppresses reporter expression below baseline, suggesting competitive promoter occupancy. Molecular dynamics simulations and AlphaFold models suggest that the IRSRKMT extension forms an -helical element stabilizing a transcriptionally productive dimer interface. Conversely, its loss disrupts quaternary assembly, alters DNA bending, and misaligns RNA polymerase-contacting residues. Furthermore, free dimers explore non-productive conformations, suggesting that functional dimerization occurs upon DNA engagement. These findings establish that a single, correctly dimerized HTH domain is sufficient for both DNA binding and transcriptional activation, providing a structural rationale for short AraC/XylS-like proteins and offering a tuneable scaffold for synthetic biology and novel anti-virulence strategies.",
  "abstract_shown": true,
  "affiliations": [
    "Departament de Bioquimica i Biologia Molecular, Universitat Autonoma de Barcelona; 08193 Cerdanyola del Valles, Spain"
  ],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 7,
  "authors": [
    {
      "name": "M. Corbella"
    },
    {
      "name": "A. Serrano"
    },
    {
      "name": "R. Bello-Madruga"
    },
    {
      "name": "M. Torrent"
    },
    {
      "name": "I. Erill"
    },
    {
      "name": "J. M. A. Blair"
    },
    {
      "affs": [
        0
      ],
      "name": "E. Sancho-Vaello"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/6d3nsw7kqgbta.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.09.23.753698",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.09.23.753698v1.full",
  "id": "6d3nsw7kqgbta",
  "issns": [],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.09.23.753698v1",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "biorxiv",
      "molecular biology"
    ],
    [
      "openalex",
      "1311|Bacterial Genetics and Biotechnology"
    ]
  ],
  "openalex": "W7214194022",
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.09.23.753698v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-23",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/6d3nsw7kqgbta.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:24:16Z",
      "native_id": "10.64898/2026.09.23.753698",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.09.23.753698v1"
    }
  ],
  "subjects": [
    {
      "field": "biochemistry",
      "origin": "biorxiv:molecular biology",
      "subfield": "molecular-biology"
    }
  ],
  "title": "Seven amino acids gate transcriptional activation by a minimal MarA Helix turn-helix DNA-binding domain",
  "title_text": "Seven amino acids gate transcriptional activation by a minimal MarA Helix turn-helix DNA-binding domain",
  "type": "preprint",
  "updated_at": "2026-10-30T12:24:16Z",
  "url": "https://research.draconitic.com/paper/6d3nsw7kqgbta",
  "venue": "bioRxiv",
  "versions": []
}