Science (2026). DOI: 10.1126/science.aed1656"> The DRT3 system found in bacteria can make double-stranded DNA with a precise alternating sequence (poly(GT/AC)). Credit: Science (2026). DOI: 10.1126/science.aed1656 Scientists at Stanford University have discovered that DRT3, a unique defense system found in bacteria, creates DNA to protect against viral infections. DRT3 is made up of two different enzymes called reverse transcriptases, Drt3a and Drt3b, and a piece of noncoding RNA (ncRNA). Together, this trio makes long, double-stranded DNA consisting of alternating repeats (GT/AC). The two proteins, Drt3a and Drt3b, each use different strategies to synthesize the two complementary strands of DNA. Drt3a sticks to the familiar playbook of copying a specific, conserved sequence of nucleic acids, in this case the ACACAC, embedded within the system's ncRNA as its blueprint. By directly reading this RNA template, it produces the corresponding poly(GT) DNA strand.…