️ Episode 172: When Random DNA Fights Back: De Novo Gene Birth as Antiphage Defense

In this episode of PaperCast Base by Base, we explore a PNAS study showing that short, previously nongenic DNA sequences can quickly evolve into genes that help bacteria survive phage attack, illuminating early steps of gene birth and the host–virus arms race. fileciteturn2file0

Study Highlights:
The authors screened two massive libraries totaling ~100 million (semi-)random open reading frames in Escherichia coli and recovered thousands of sequences that improved survival during T4 phage challenge. A set of short proteins, dubbed Random Inhibitors of Phage infection (Rips), broadly protected cells by activating the Rcs envelope-stress pathway and triggering colanic-acid capsule production that physically blocks adsorption. A second class of hits, Random T4 Inhibitor Products (rtp1–4), acted with specificity by reducing expression of the OmpC outer-membrane receptor, thereby limiting T4 and other OmpC-dependent phage entry; for some rtp genes the protective molecule was RNA rather than protein. Transcriptomics, reporter assays, and adsorption measurements supported these mechanisms while showing minimal growth penalties, and evolved T4 variants rapidly gained baseplate mutations that restored adsorption and infectivity.

Conclusion:
Random sequence space harbors many routes to immediate fitness gains, with de novo protein- and RNA-based functions rewiring bacterial envelopes and receptors in ways that both reveal mechanisms of gene birth and suggest new antiphage strategies.

Reference:
Frumkin I, Vassallo CN, Chen YH, Laub MT. Emergence of antiphage functions from random sequence libraries reveals mechanisms of gene birth. Proceedings of the National Academy of Sciences. 2025;122(42):e2513255122. https://doi.org/10.1073/pnas.2513255122 fileciteturn2file0

License:
This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/

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