美国加州大学圣迭戈分校Partho Ghosh研究小组揭示反转录过程在多样性生成逆转录元件中的RNA控制。相关论文于2025年1月8日在线发表在《自然》杂志上。

研究人员表示，多样性生成反转录元件（DGR）在生态多样的微生物中创造了巨大的蛋白质序列变异（最多可达10³⁰）。最近的一项调查发现，来自1500多个细菌和古菌属的大约31000个DGR，涵盖了超过90种环境类型。DGR在人体肠道微生物群中尤为丰富，并且在纳米级微生物中也得到了丰富，这些微生物似乎构成了大多数微生物生命，并且尽管基因组减少，仍然保持着DGR。DGR还与多细胞生物的出现有关。

变异发生在蛋白质编码RNA模板的反转录过程中，伴随腺苷的错误掺入。在典型的博德氏百日咳噬菌体DGR中，模板必须被上下游的RNA片段包围，以便通过DGR反转录酶bRT和相关蛋白Avd的复合物进行互补DNA合成。周围RNA的功能此前未知。

研究人员通过冷冻电子显微镜展示了这种RNA如何包围bRT并位于桶状的Avd上，形成亲密的核糖核蛋白。核糖核蛋白中大量必要的相互作用精确地将RNA同源二聚体定位到bRT的活性位点，从而启动反转录。这些结果解释了周围的RNA如何启动互补DNA合成，促进过程性，终止聚合，并通过可能在远缘分类群中的DGR中保守的机制严格限制突变发生在特定的蛋白质上。

附：英文原文

Title: RNA control of reverse transcription in a diversity-generating retroelement

Author: Handa, Sumit, Biswas, Tapan, Chakraborty, Jeet, Ghosh, Gourisankar, Paul, Blair G., Ghosh, Partho

Issue&Volume: 2025-01-08

Abstract: Diversity-generating retroelements (DGRs) create massive protein sequence variation (up to 1030)1 in ecologically diverse microorganisms. A recent survey identified around 31,000 DGRs from more than 1,500 bacterial and archaeal genera, constituting more than 90 environment types2. DGRs are especially enriched in the human gut microbiome2,3 and nano-sized microorganisms that seem to comprise most microbial life and maintain DGRs despite reduced genomes4,5. DGRs are also implicated in the emergence of multicellularity6,7. Variation occurs during reverse transcription of a protein-encoding RNA template coupled to misincorporation at adenosines. In the prototypical Bordetella bacteriophage DGR, the template must be surrounded by upstream and downstream RNA segments for complementary DNA synthesis to be carried out by a complex of the DGR reverse transcriptase bRT and associated protein Avd. The function of the surrounding RNA was unknown. Here we show through cryogenic electron microscopy that this RNA envelops bRT and lies over the barrel-shaped Avd, forming an intimate ribonucleoprotein. An abundance of essential interactions in the ribonucleoprotein precisely position an RNA homoduplex in the bRT active site for initiation of reverse transcription. Our results explain how the surrounding RNA primes complementary DNA synthesis, promotes processivity, terminates polymerization and strictly limits mutagenesis to specific proteins through mechanisms that are probably conserved in DGRs belonging to distant taxa.

DOI: 10.1038/s41586-024-08405-w

Source: https://www.nature.com/articles/s41586-024-08405-w