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The iscS Gene is Essential for the Biosynthesis of 2-Selenouridine in tRNA and the Selenocysteine-Containing Formate Dehydrogenase H
Hisaaki Mihara, Shin-ichiro Kato, Gerard M. Lacourciere, Thressa C. Stadtman, Robert A. J. D. Kennedy, Tatsuo Kurihara, Umechiyo Tokumoto, Yasuhiro Takahashi and Nobuyoshi Esaki
Proceedings of the National Academy of Sciences of the United States of America
Vol. 99, No. 10 (May 14, 2002), pp. 6679-6683
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/3058725
Page Count: 5
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Three NifS-like proteins, IscS, CSD, and CsdB, from Escherichia coli catalyze the removal of sulfur and selenium from L-cysteine and L-selenocysteine, respectively, to form L-alanine. These enzymes are proposed to function as sulfur-delivery proteins for iron-sulfur cluster, thiamin, 4-thiouridine, biotin, and molybdopterin. Recently, it was reported that selenium mobilized from free selenocysteine is incorporated specifically into a selenoprotein and tRNA in vivo, supporting the involvement of the NifS-like proteins in selenium metabolism. We here report evidence that a strain lacking IscS is incapable of synthesizing 5-methylaminomethyl-2-selenouridine and its precursor 5-methylaminomethyl-2-thiouridine (mnm5s 2U) in tRNA, suggesting that the sulfur atom released from L-cysteine by the action of IscS is incorporated into mnm5s 2U. In contrast, neither CSD nor CsdB was essential for production of mnm5s 2U and 5-methylaminomethyl-2-selenouridine. The lack of IscS also caused a significant loss of the selenium-containing polypeptide of formate dehydrogenase H. Together, these results suggest a dual function of IscS in sulfur and selenium metabolism.
Proceedings of the National Academy of Sciences of the United States of America © 2002 National Academy of Sciences