SECIS元件

SECIS元件全稱為硒半胱氨酸插入序列（SElenoCysteine Insertion Sequence），是生物mRNA中一個長約60nt的RNA元件，次級結構為一莖環^[1] ，此元件會使核糖體轉譯時不將UGA當作終止密碼子，而將其作為編碼特殊胺基酸硒半胱氨酸的密碼子，因此為編碼硒蛋白的mRNA所需。三域生物皆有SECIS元件^[2][3][4][5]，雖皆為莖環結構，但彼此序列差異很大（不過洛基古菌（英語：Lokiarchaeota）的SECIS元件序列和真核生物的較為接近）^[6]，細菌的SECIS元件通常緊跟在UGA密碼子之後，真核生物與古菌的SECIS元件則位於mRNA的3'非轉譯區，可使mRNA中多於一個UGA密碼子編碼硒半胱氨酸，另外已知甲烷球菌屬的一種古菌具有位於5'非轉譯區的SECIS元件^[7][8]。真核生物的SECIS元件通常有特殊的A：G鹼基配對，可能對其功能相當重要^[9]。SECIS元件結合蛋白2（SECIS-binding protein 2，簡稱SBP2）可與SECIS元件結合以促進UGA密碼子編碼硒半胱氨酸^[10]，並可避免mRNA被無義介導的mRNA降解（NMD）途徑降解移除^[11]。

SECIS元件
一個SECIS元件可能的次級結構，鹼基標示為依循IUPAC規則
識別符
代號	SECIS_1
Alt.代號	SECIS
Rfam	RF00031
其他數據
RNA類型	順式作用元件

目前已有數個生物資訊學軟件可用於尋找基因組中的SECIS元件，有助於尋找新的硒蛋白^[12]。

參考文獻

• 分子與細胞生物學主題

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2. Mix H, Lobanov AV, Gladyshev VN. SECIS elements in the coding regions of selenoprotein transcripts are functional in higher eukaryotes. Nucleic Acids Research. 2007, 35 (2): 414–423. PMC 1802603 . PMID 17169995. doi:10.1093/nar/gkl1060.
3. Cassago A, Rodrigues EM, Prieto EL, Gaston KW, Alfonzo JD, Iribar MP, Berry MJ, Cruz AK, Thiemann OH. Identification of Leishmania selenoproteins and SECIS element. Molecular and Biochemical Parasitology. October 2006, 149 (2): 128–134. PMID 16766053. doi:10.1016/j.molbiopara.2006.05.002.
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6. Mariotti, Marco; Lobanov, Alexei V.; Manta, Bruno; Santesmasses, Didac; Bofill, Andreu; Guigó, Roderic; Gabaldón, Toni; Gladyshev, Vadim N. Lokiarchaeota Marks the Transition between the Archaeal and Eukaryotic Selenocysteine Encoding Systems. Molecular Biology and Evolution. 2016, 33 (9): 2441–2453. ISSN 0737-4038. doi:10.1093/molbev/msw122.
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11. Chellan B, Zhao L, Landeche M, Carmean CM, Dumitrescu AM, Sargis RM. Selenocysteine insertion sequence binding protein 2 (Sbp2) in the sex-specific regulation of selenoprotein gene expression in mouse pancreatic islets.. Sci Rep. 2020, 10 (1): 18568. PMC 7596060 . PMID 33122797. doi:10.1038/s41598-020-75595-4.
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