Bacteria manufacturing DNA

Cells usually copy DNA from another DNA or RNA strand. A Science paper published April 16 reports a bacterial enzyme that built a specific DNA sequence by using its own protein structure as the guide. (science.org) The study came from Alex Gao’s lab at Stanford University and focused on DRT3, a bacterial anti-phage system made of two reverse transcriptases, called Drt3a and Drt3b, plus a noncoding RNA. PubMed lists the paper as “Protein-templated synthesis of dinucleotide repeat DNA by an antiphage reverse transcriptase,” by Pujuan Deng and colleagues in Science. (pubmed.ncbi.nlm.nih.gov) Here is the basic rule the paper tests: polymerases are the enzymes that write DNA or RNA, and they normally do it by reading an existing nucleic-acid template, one chemical “letter” at a time. The Science abstract says Drt3b instead made a complementary poly(AC) DNA strand “in the complete absence of a nucleic acid template.” (science.org) The system did not make arbitrary DNA. The paper says DRT3 produced alternating poly(GT/AC) double-stranded DNA, with Drt3a writing one strand from the noncoding RNA and Drt3b writing the matching strand through conserved amino-acid residues in its active site. (science.org) Nature covered an earlier preprint from the same line of work in May 2024 and described the finding as bacteria “writing new genes,” a sign that biologists had already started debating how broadly the result fits with standard textbook models. That 2024 report pointed to bacterial defense systems as a source of exceptions to the usual DNA-to-RNA-to-protein flow. (nature.com) Outside experts quoted by the Centre for Genomic Regulation’s CobcV site said the mechanism could mark “a significant conceptual shift,” while also stressing that the biology is still being worked out. The same report said researchers do not yet know exactly how DRT3 stops phages after making this DNA. (cobcv.com) That uncertainty matters because the paper changes one part of the story more clearly than the rest. It shows a route to sequence-specific DNA synthesis that does not rely on a DNA or RNA template, but it does not yet settle how widespread that strategy is in nature or what full job the product DNA performs inside infected bacteria. (science.org) The claim spread quickly online after Catharine Young highlighted it on X, where her post linked the paper and framed it as a challenge to a basic rule of molecular biology. The paper itself is now the key document to watch, because replication by other labs will decide whether this bacterial trick becomes a new textbook example or a specialized exception. (x.com)