Scientists find bacteria make DNA differently
- Stanford researchers reported on April 16 that a bacterial anti-phage enzyme called DRT3 can build one DNA strand without copying DNA or RNA. - In Science, the team showed DRT3 makes alternating poly(GT/AC) DNA; cryo-electron microscopy resolved a 6:6:6 Drt3a-Drt3b-RNA complex at 2.6 angstroms. - The work extends recent reports that bacterial reverse transcriptases can assemble antiviral DNA products in unexpected ways. (science.org)
Cells usually copy DNA the way a scribe copies text: one strand is read, and a matching strand is written from that template. A Science paper published April 16 reports a bacterial enzyme that breaks that rule for one half of the job. (science.org) (pubmed.ncbi.nlm.nih.gov) The enzyme system is called DRT3, short for a defense-associated reverse transcriptase found in bacteria that fight off bacteriophages, the viruses that infect bacteria. The Stanford team reported that DRT3 synthesizes alternating poly(GT/AC) double-stranded DNA. (science.org) (biochemistry.stanford.edu) One DRT3 subunit, Drt3a, still works in the familiar way. It uses a short ACACAC sequence in a noncoding RNA molecule as a template to build the poly(GT) strand. (science.org) (pubmed.ncbi.nlm.nih.gov) The surprise is the partner subunit, Drt3b. The paper says Drt3b builds the complementary poly(AC) strand in the complete absence of a DNA or RNA template, using its own active-site amino acids to enforce the A-C-A-C pattern. (science.org) (pubmed.ncbi.nlm.nih.gov) To show that, the researchers used cryo-electron microscopy, a method that freezes molecules and images them at near-atomic scale. They resolved a D3-symmetric complex containing six copies each of Drt3a, Drt3b, and the noncoding RNA at 2.6 angstrom resolution. (science.org) (pubmed.ncbi.nlm.nih.gov) That matters because biology textbooks usually sort nucleic-acid-building enzymes into two camps: template-directed polymerases that copy an existing sequence, and template-independent enzymes that add simpler, less specific tracts. The new paper places Drt3b outside that neat split by showing sequence-specific DNA synthesis guided by protein structure. (science.org) The finding also fits a fast-moving story in bacterial immunity. In 2024, another Science paper showed a different defense-associated reverse transcriptase, DRT2, can make a new antiviral gene from a noncoding RNA during phage infection. (science.org) Together, the studies suggest bacteria carry a wider toolkit for making defensive DNA than researchers had recognized. Stanford’s biochemistry department said the new DRT3 work was led by Pujuan Deng, Hyunbin Lee, Carlo Armijo, Haoqing Wang, and Alex Gao. (biochemistry.stanford.edu) (science.org) The paper does not say this rewrites all DNA replication in cells; it describes a specialized anti-phage system in bacteria. But it does add one more way that living systems can write genetic material when viruses attack. (science.org)
