Selenium-dependent gene regulation in Archaea

硒是生命三个领域的许多成员所必需的微量元素，但硒是如何运输到细胞中的尚不清楚。硒通过共翻译插入的氨基酸硒半胱氨酸(Sec)和tRNA修饰的2-硒尿苷(Seu)发挥其生物学功能。产甲烷古细菌甲烷球菌在其中枢能量代谢中使用含SEC的蛋白质，即水基因营养产甲烷作用。然而，当缺乏硒时，会诱导一组不依赖于硒的同工酶，使生长不依赖于这种微量元素。然而，细胞中的硒状态是如何被感知的，以及这种信息是如何被转导来改变基因表达的，目前还不清楚。作为Sec和Seu的生物合成前体，硒磷酸盐是代表细胞硒状态的一个很有吸引力的候选者。此外，对maripaludis突变体的表型分析表明，LysR型转录调控因子HrsM参与了硒依赖的硒蛋白基因的激活和同源基因的抑制，但HrsM依赖的基因调控机制尚不清楚。为了阐明Maripaludis如何(以及以何种形式)将硒转运到细胞内，确定代表细胞硒状态的代谢线索，并揭示HrsM以一种依赖于硒的方式激活或抑制基因表达的机制，是拟议项目的目标。

Selenium is an essential trace element for many members of all three domains of life, but how selenium is transported into cells is unknown. Selenium exerts its biological function through the co-translationally inserted amino acid selenocysteine (Sec) and the tRNA modification 2-selenouridine (SeU). The methanogenic archaeon Methanococcus maripaludis employs Sec-containing proteins in its central energy metabolism, hydrogenotrophic methanogenesis. However, when selenium is scarce, a set of selenium-independent isoenzymes is induced, rendering growth independent of this trace element. However, how the cellular selenium status is sensed, and how this information is transduced to alter gene expression is unknown. Selenophosphate, which is the biosynthetic precursor of both Sec and SeU, is an attractive candidate for representing the cellular selenium status. Furthermore, phenotypic analyses of M. maripaludis mutants suggest involvement of the LysR-type transcription regulator HrsM in selenium-dependent activation of the selenoprotein genes and repression of the isogenes, but the mechanism of HrsM-dependent gene regulation is unknown. To elucidate how (and in what form) M. maripaludis transports selenium into the cell, to define the metabolic cue representing the cellular selenium status, and to unravel the mechanism HrsM either activates or represses gene expression in a selenium-dependent manner, is the aim of the proposed project.