Bacteria shown making protein DNA
- Stanford researchers reported in Science that a bacterial antiphage system called DRT3 can build one DNA strand from an RNA template and the matching strand from the protein itself. - The team said DRT3 forms a 6:6:6 complex and makes alternating poly(GT/AC) DNA; one subunit, Drt3b, writes the poly(AC) strand without any nucleic-acid template. - The finding extends a fast-growing list of bacterial reverse-transcriptase defenses, after 2025 and 2026 studies showed related systems making poly-dA and other antiviral DNA products. (nature.com)
DNA copying usually means reading DNA or RNA as a template. A Science paper says one bacterial antiviral enzyme can instead use its own protein shape to specify part of a DNA sequence. (science.org) The system is called DRT3, short for defense-associated reverse transcriptase 3. Pujuan Deng, Hyunbin Lee, Carlo Armijo, Haoqing Wang and Alex Gao’s team at Stanford reported that it helps bacteria resist phage, the viruses that infect bacteria. (science.org) Most polymerases work like copiers: bases in DNA or RNA tell the enzyme which base comes next. In DRT3, one subunit called Drt3a still follows that familiar rule by reading a conserved ACACAC sequence in a noncoding RNA. (science.org) The surprise is the partner subunit, Drt3b. The paper says Drt3b makes the complementary poly(AC) strand in the complete absence of a nucleic-acid template, using protein contacts in its active site to enforce the A-C-A-C pattern. (science.org 1) (science.org 2) The full machine is large and highly ordered. Cryo-electron microscopy at 2.6 angstrom resolution showed a D3-symmetric complex containing six copies each of Drt3a, Drt3b and the noncoding RNA. (science.org) That places the work inside a broader shift in bacterial immunity research. Scientists have spent the past two years showing that several defense-associated reverse transcriptases do not just copy genes; they manufacture unusual DNA products during phage attack. (science.org) (nature.com) In a 2025 Nature paper, a related system called DRT9 was shown to make long polydeoxyadenylate, or poly-dA, after viral infection. That DNA buildup drove abortive infection, a self-sacrifice strategy in which an infected bacterium stops growing so the phage cannot spread. (nature.com) A separate 2026 preprint described DRT7, a reverse transcriptase-primase system that the authors said makes long, protein-primed poly(A)/poly(T)-rich duplex-like DNA after phage activation. That study has not yet been peer reviewed. (biorxiv.org) Nature reported on April 2 that researchers are now mining bacterial genomes for thousands of antiviral defense proteins that could become molecular biology tools. DRT3 adds a new mechanism to that search: sequence-specific DNA synthesis directed partly by protein rather than by nucleic acid. (nature.com) (science.org) The immediate result is narrower than “bacteria make DNA from protein” sounds. The paper describes an antiphage reverse transcriptase making a repetitive alternating strand, not a general-purpose enzyme that can write any DNA sequence on demand. (science.org) Even so, the core claim is direct: part of DRT3’s antiviral DNA product is specified by the enzyme’s own structure. For a field built on template copying, that is a new way for bacteria to write DNA under viral attack. (science.org)
