{
  "abstract": "Retrons are unique among bacterial defence systems in using DNA to sense phage infection. They achieve this by producing multicopy single-stranded DNA (msDNA) that monitors the activity of DNA-targeting phage proteins. Although we understand how extensive msDNA perturbations such as degradation activate retrons, activation by subtle chemical modifications remains enigmatic. Here, we used a structure-function approach to elucidate how single-site msDNA methylation activates Retron-Sen2. The cryo-EM structure of Retron-Sen2 features RcaT, the most prevalent retron effector, sequestered as an inactive dimer within a four-component assembly of previously undescribed architecture. Methylation by DNA adenine methyltransferase disrupts the RcaT-msDNA interaction and exposes a previously occluded interface that enables RcaT dimers to form tetramers, leading to retron disassembly. We show that RcaT dimer-dimer assembly is essential for its toxicity. To assess whether this is a conserved RcaT feature, we characterised additional homologues. RcaTs capable of tetramerisation or higher-order oligomerisation are toxic and form distinct phylogenetic clades from RcaTs that remain dimeric and are non-toxic. Together, our findings provide a paradigm for retron activation by single-site msDNA modifications and showcase how variation in an intrinsic protein property can diversify the toxicity of the same bacterial defence effector during evolution.",
  "abstract_shown": true,
  "affiliations": [
    "European Molecular Biology Laboratory (EMBL)"
  ],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 9,
  "authors": [
    {
      "name": "P. Spatharas"
    },
    {
      "name": "A. L. J. Yang"
    },
    {
      "name": "E. Mullapudi"
    },
    {
      "name": "G. Chojnowski"
    },
    {
      "name": "F. Corona"
    },
    {
      "name": "D. Kumar"
    },
    {
      "name": "J. Bobonis"
    },
    {
      "affs": [
        0
      ],
      "name": "A. Typas"
    },
    {
      "name": "M. Wilmanns"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/58wyb3rm0zcqy.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.10.13.758329",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.10.13.758329v1.full",
  "id": "58wyb3rm0zcqy",
  "issns": [],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.10.13.758329v1",
  "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",
      "microbiology"
    ],
    [
      "openalex",
      "2303|Bacteriophages and microbial interactions"
    ]
  ],
  "openalex": "W7221716391",
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.10.13.758329v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-13",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/58wyb3rm0zcqy.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:27:38Z",
      "native_id": "10.64898/2026.10.13.758329",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.10.13.758329v1"
    }
  ],
  "subjects": [
    {
      "field": "biology",
      "origin": "biorxiv:microbiology",
      "subfield": "microbiology"
    }
  ],
  "title": "Single-site DNA methylation activates retron defence by enabling effector tetramerisation",
  "title_text": "Single-site DNA methylation activates retron defence by enabling effector tetramerisation",
  "type": "preprint",
  "updated_at": "2026-10-30T12:27:38Z",
  "url": "https://research.draconitic.com/paper/58wyb3rm0zcqy",
  "venue": "bioRxiv",
  "versions": []
}