Division of Applied Chemistry, Graduate School of Sciences and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611, Japan.
Division of Electrical, Electronic and Information Engineering, Graduate School of Sciences and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611, Japan.
Biochim Biophys Acta Gene Regul Mech. 2023 Dec;1866(4):194982. doi: 10.1016/j.bbagrm.2023.194982. Epub 2023 Sep 1.
Introns can enhance gene expression in eukaryotic cells in a process called intron-mediated enhancement (IME). The levels of enhancement are affected not only by the intron sequence but also by coding sequences (CDSs). However, the parts of CDSs responsible for mediating IME have not yet been identified. In this study, we identified an IME-mediating sequence by analyzing three pairs of IME-sensitive and -insensitive CDSs in Saccharomyces cerevisiae. Expression of the CDSs yCLuc, yRoGLU1, and KmBGA1 was enhanced by the presence of an intron (i.e., they were IME sensitive), but the expression of each corresponding codon-changed CDS, which encoded the identical amino acid sequence, was not enhanced (i.e., they were IME insensitive). Interestingly, the IME-insensitive CDSs showed higher expression levels that were like intron-enhanced expression of IME-sensitive CDSs, suggesting that expression of IME-sensitive CDSs was repressed. A four-nucleotide sequence (TCTT) located in the promoter-proximal position of either the untranslated or coding region was found to be responsible for repression in IME-sensitive CDSs, and repression caused by the TCTT sequence was relieved by the presence of an intron. Further, it was found that the expression of intron-containing yeast-native genes, UBC4 and MPT5, was repressed by TCTT in the CDS but relieved by the introns. These results indicate that TCTT sequences in promoter-proximal positions repress gene expression and that introns play a role in relieving gene repression caused by sequences such as TCTT.
内含子可以通过一种称为内含子介导增强（IME）的过程增强真核细胞中的基因表达。增强的水平不仅受内含子序列的影响，还受编码序列（CDS）的影响。然而，负责介导 IME 的 CDS 部分尚未确定。在这项研究中，我们通过分析酿酒酵母中三对 IME 敏感和不敏感的 CDS 来鉴定 IME 介导的序列。CDS 的表达被内含子增强（即它们是 IME 敏感的），但每个相应的密码子改变 CDS 的表达没有被增强（即它们是 IME 不敏感的）。有趣的是，IME 不敏感的 CDS 表现出更高的表达水平，类似于 IME 敏感的 CDS 的内含子增强表达，表明 IME 敏感的 CDS 的表达受到抑制。发现在非翻译或编码区的启动子近端位置存在一个四核苷酸序列（TCTT）负责 IME 敏感 CDS 中的抑制，并且内含子的存在缓解了 TCTT 序列引起的抑制。此外，还发现含有内含子的酵母天然基因 UBC4 和 MPT5 的表达在 CDS 中受到 TCTT 的抑制，但被内含子缓解。这些结果表明，启动子近端位置的 TCTT 序列抑制基因表达，内含子在缓解 TCTT 等序列引起的基因抑制方面发挥作用。
