Polθ reverse transcribes RNA and promotes RNA-templated DNA repair

Genome-embedded ribonucleotides arrest replicative DNA polymerases (Pols) and cause DNA breaks. Whether mammalian DNA repair Pols efficiently use template ribonucleotides and promote RNA-templated DNA repair synthesis remains unknown. We find that human Pol theta reverse transcribes RNA, similar to retroviral reverse transcriptases (RTs). Pol theta exhibits a significantly higher velocity and fidelity of deoxyribonucleotide incorporation on RNA versus DNA. The 3.2-angstrom crystal structure of Pol. on a DNA/RNA primer-template with bound deoxyribonucleotide reveals that the enzyme undergoes a major structural transformation within the thumb subdomain to accommodate A-form DNA/RNA and forms multiple hydrogen bonds with template ribose 2'-hydroxyl groups like retroviral RTs. Last, we find that Pol. promotes RNA-templated DNA repair in mammalian cells. These findings suggest that Pol theta was selected to accommodate template ribonucleotides during DNA repair.

Automated summary

The study reveals that human Pol theta can reverse transcribe RNA, incorporate deoxyribonucleotides on RNA with higher velocity and fidelity, and promote RNA-templated DNA repair synthesis in mammalian cells, suggesting that Pol theta was selected to accommodate template ribonucleotides during DNA repair.