Science published a collaborative research study on May 22 by Professor Zhu Bin's team from the School of Life Science and Technology at Huazhong University of Science and Technology (HUST), and Professor Wang Longfei's team from the School of Pharmaceutical Sciences at Wuhan University in its First Release format. The study, titled "DNA Polymerization Activates RNA Cleavage of an RT-like Antiviral Enzyme", marks the first discovery of a multifunctional antiviral nuclease, DRT4, which is activated by DNA synthesis to cleave RNA.

In recent years, a type of immune system known as Defense-associated Reverse Transcriptase (DRT) has garnered widespread attention. While known systems such as DRT2, DRT3, and DRT9 exhibit unconventional DNA synthesis capabilities, their antiviral effects have remained dependent on the core function of reverse transcriptase – DNA synthesis. This raises a critical scientific question: Are there members within the DRT family capable of achieving immune defense through novel functions beyond DNA synthesis?

Since 2020, Professor Zhu Bin's team has focused on exploring novel antiviral mechanisms of the DRT system, advancing research on the biological functions of the DRT family. The team has now made a significant breakthrough: DRT4 not only exhibits DNA polymerase activity, but also possesses dual nuclease functions as a DNA exonuclease and RNA endonuclease. The study has, for the first time, confirmed that RNA cleavage is the core mechanism underlying the antiviral effects of the DRT system.

Through structural biology studies, the team elucidated the complete mechanism by which DRT4 transitions its molecular activity, and achieves an antiviral function. Under normal conditions, the polymerase and exonuclease activities of DRT4 maintain a dynamic balance, keeping the system in a dormant state. Following phage invasion, the intracellular dNTP concentration increases, promoting sustained DNA synthesis and extension. This triggers a conformational rearrangement of the protein, creating a novel RNA endonuclease active site. This site cleaves both host and phage RNA, halting cellular metabolism and blocking viral replication.

This study is the first to confirm that the DRT system exerts its antiviral effects through RNA cleavage, expanding the functional boundaries of the DRT family and suggesting that other family members may possess unknown immune defense functions. The research demonstrates that reverse transcriptases can perform both nucleic acid synthesis and cleavage, highlighting the evolutionary plasticity of molecular machinery in life, and underscoring its pivotal role in the evolution of nucleic acid metabolism.

More importantly, this work fills a critical mechanistic gap in the study of the DRT system, establishing a comprehensive immune model that forms a closed loop of "signal sensing, safety regulation, and effector response".

Rong Xuejun, PhD from HUST; Xiao Jun, PhD from Wuhan University; Zhao Xinyuan and Yan Yan, PhD from HUST; and Li Jing, PhD from Wuhan University are co-first authors of the paper. Professors Zhu Bin and Wang Longfei; and Wang Xionglue, PhD from HUST, are co-corresponding authors, with HUST listed as the first affiliation of the paper.

Professor Zhu Bin's research group focuses on the natural history of nucleases, uncovering unprecedented nuclease functions, investigating novel biological mechanisms involving unique nucleases, and developing their applications. In recent years, the team has discovered multiple new types of nucleases and, based on these findings, elucidated the mechanisms of novel prokaryotic immune systems such as Gabija, E2-CBASS, and DRT4. Their research has been published in a number of prestigious journals, including Science, Nature, Nature Microbiology, and Cell Host & Microbe. The group's original discoveries have been commercialized by relevant enterprises into RNA synthesis enzymatic tools such as Ice LakeTM RNA polymerase, Clean T7TM RNA polymerase, and T7 RNA polymerase 2.0.

Source: School of Life Science and Technology, HUST