Bacterial defense system builds DNA in unexpected new way to stop viruses

Key Points:

• Stanford scientists discovered that the bacterial defense system DRT3 creates long, double-stranded DNA with alternating GT/AC repeats to protect against viral infections, using two enzymes, Drt3a and Drt3b, and a noncoding RNA.
• Drt3a synthesizes one DNA strand by copying an RNA template, while Drt3b uniquely builds the complementary strand without a nucleic acid template, instead using its own protein structure as a mold.
• The DRT3 system was found in at least 20 bacterial species and was shown to effectively defend E. coli against viruses by activating only upon detecting a specific viral protein, ST61.
• Cryo-electron microscopy revealed that DRT3 forms a symmetrical hexamer complex composed of six Drt3a, six Drt3b proteins, and six noncoding RNAs, highlighting a novel protein-templated DNA synthesis mechanism.
• This discovery challenges previous assumptions about DNA synthesis and could lead to new biotechnological and medical applications by harnessing bacteria's protein-templated DNA production for viral defense.