环状RNA是一种由线状RNA环化而成的非编码RNA，广泛存在于从酵母到人的各种真核生物中，具有调控基因转录的重要功能。然而，目前尚无确切报道证明细菌中存在环状RNA，其合成机制和功能也完全未知。我们在前期研究中发现，大肠杆菌中存在环状RNA（主要由rRNAs环化而成），且在不同抗生素压力下表达的种类和数量存在明显差异，推测其可能参与抗生素压力下细菌生长调控。本课题将以大肠杆菌为样本：1）证实细菌中存在环状RNA；2）通过同源重组构建各种RNA操作酶缺失的突变菌株，以及改变环化位点附近的茎环配对序列，来发现其合成机制；3）通过转录组测序观察不同抗生素条件下环状RNA的种类和数量变化，分析其在调控细胞生长、应对抗生素压力中的作用，并发现其中的关键环状RNA，再通过过表达和表达抑制实验证实其作用。通过上述研究，本课题将系统证明细菌中是否存在环状RNA，并阐释其合成机制和生物学功能。

Circular RNAs (circRNAs) are a class of non-coding RNA produced by direct ligation of 3’ end and 5’ end of linear RNAs. Recent studies show that circRNAs are abundant across the eukaryotic tree of life, and have important function in regulating gene expression. However, little research has been done on the circRNAs in bacteria, so the biogenesis as well as functions of circRNAs in bacteria remain uncovered. In our recent work, we detected circRNAs (mainly circular rRNAs) in the E.coli, and there are remarkable difference in the quantity and species of circRNAs at various ceftriaxone concentration, which indicates that circRNAs may play a role in regulating bacterial growth and helping survival at antibiotic stress. We plan to solve the following three problems in this project: 1) Validate the existence of circRNAs in bacteria with various methods. 2) Explore the biogenesis of circRNAs in bacteria by constructing mutant strains in RNase or RNA ligase or flanking sequence of junction sites. 3) Identify the roles of circRNAs in growth regulation and response to antibiotics. To achieve this, we will investigate the circRNAs profile in various concentrates of different kinds of antibiotics and verify the roles of key circRNAs through overexpression and knockdown experiments. In this project, we will verify the existence of circRNAs in bacteria, and characterize their biosynthesis as well as functions in growth regulation and response to antibiotics.