Defense associated reverse transcriptase

Defense-associated reverse transcriptase (DRT) ribonucleoprotein complexes are a class of prokaryotic antiviral systems composed of reverse transcriptase enzymes and associated non-coding RNAs (ncRNAs). These complexes function as part of bacterial and archaeal defense mechanisms against bacteriophage infection and are characterized by their ability to synthesize nucleic acids.[1]

DRT systems belong to a broader group of reverse transcriptase (RT) associated defense elements.[2] Unlike classical reverse transcriptases, which copy RNA into DNA using standard template dependent mechanisms, DRT complexes frequently employ hybrid strategies involving RNA templates, protein templating, or template-independent polymerization.[3]

DRT features

DRT ribonucleoprotein complexes typically include one or more reverse transcriptase proteins and a structured ncRNA. The ncRNA component plays multiple roles: template for DNA synthesis, structural scaffold for assembly of the complex and regulatory element controlling enzymatic activity.

DRT ribonucleoprotein complexes share features with several well-known biological systems:

Unlike this ribonucleoprotein complexes, DRT use protein-templated synthesis and produce repetitive DNA products.[3]

Representative DRT systems

DRT2

DRT2 systems produce long repetitive complement DNA concatemers, in some cases assembling sequences not directly encoded in the genome. The associated ncRNA is thought to contribute to the synthesis process, acting as a template or structural guide.[4]

DRT3

DRT3 consists of two distinct reverse transcriptases Drt3a and Drt3b and an structured ncRNA. The ncRNA contains a conserved ACACAC motif that acts as a template for DNA synthesis.

Drt3a synthesizes a poly(GT) DNA strand using the ncRNA template while Drt3b synthesizes the complementary poly(AC) strand without a nucleic acid template, using a protein-templated mechanism. This system produces double-stranded repetitive DNA.[3]

DRT9

DRT9 systems synthesize poly(A)-rich DNA products and are also associated with an ncRNA component. Structural studies have shown that the ncRNA is required for assembly and activation of the complex, mediates oligomerization of the reverse transcriptase.[5]

Mechanism of action

DRT complexes are generally activated during phage infection. They use reverse transcriptase activity to synthesize DNA or RNA products that interfere with phage replication or viability. Distinctive mechanistic features include:

  • RNA-templated DNA synthesis (similar to telomerase)
  • Template-independent polymerization
  • Protein-templated nucleotide incorporation
  • Generation of repetitive or low-complexity nucleic acid products[3]

References

  1. ^ Gao, L. (2020). "Diverse enzymatic activities mediate antiviral immunity in prokaryotes". Science. 369 (6507): 1077–1084. Bibcode:2020Sci...369.1077G. doi:10.1126/science.aba0372. PMC 7985843. PMID 32855333.
  2. ^ Mestre, M.R. (2022). "A highly diverse family of prokaryotic reverse transcriptases associated with defense functions". Nucleic Acids Research. 50 (11): 6084–6101. doi:10.1093/nar/gkac467. PMC 9226505. PMID 35648479.
  3. ^ a b c d Deng, P. (2026). "Protein-templated synthesis of dinucleotide repeat DNA by an antiphage reverse transcriptase". Science eaed1656. doi:10.1126/science.aed1656. PMID 41990131.
  4. ^ Wilkinson, M.E. (2024). "Phage-triggered reverse transcription assembles a toxic repetitive gene from a noncoding RNA". Science. 386 (6717) eadq3977. Bibcode:2024Sci...386q3977W. doi:10.1126/science.adq3977. PMC 12039810. PMID 39208082.
  5. ^ Tang, S. (2025). "Antiviral reverse transcriptases reveal the evolutionary origin of telomerase". bioRxiv 10.1101/2025.10.16.682844.

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