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體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.
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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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