One Polypeptide with Two Aminoacyl-tRNA Synthetase Activities

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Science  21 Jan 2000:
Vol. 287, Issue 5452, pp. 479-482
DOI: 10.1126/science.287.5452.479

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The genome sequences of certain archaea do not contain recognizable cysteinyl–transfer RNA (tRNA) synthetases, which are essential for messenger RNA–encoded protein synthesis. However, a single cysteinyl–tRNA synthetase activity was detected and purified from one such organism, Methanococcus jannaschii. The amino-terminal sequence of this protein corresponded to the predicted sequence of prolyl–tRNA synthetase. Biochemical and genetic analyses indicated that this archaeal form of prolyl–tRNA synthetase can synthesize both cysteinyl-tRNACys and prolyl-tRNAPro. The ability of one enzyme to provide two aminoacyl-tRNAs for protein synthesis raises questions about concepts of substrate specificity in protein synthesis and may provide insights into the evolutionary origins of this process.

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