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Role of Ribothymidine in Mammalian tRNAPhe

Bruce A. Roe and Hau-Yang Tsen
Proceedings of the National Academy of Sciences of the United States of America
Vol. 74, No. 9 (Sep., 1977), pp. 3696-3700
Stable URL: http://www.jstor.org/stable/67017
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Role of Ribothymidine in Mammalian tRNAPhe
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Abstract

We have previously reported that mammalian tRNAsPhe from various tissues contain different amounts of ribothymidine and that a uridine methylase from Escherichia coli can quantitatively convert these tRNAs to species that contain their full complement of ribothymidine at position 23 from the 3′ terminus. The role of ribothymidine in mammalian tRNAs has now been investigated by studying the ability of several highly purified mammalian tRNAsPhe, differing only in their ribothymidine content, to support poly(U)-directed poly(Phe) synthesis under various conditions. Our results indicate that the ribothymidine content of mammalian tRNAPhe can be correlated with the ability of these tRNAs to function in vitro in a low-magnesium (6 mM), ribosome wash factor-dependent, poly(U)-directed poly(Phe) synthesis system from rat liver. Specifically, the effect of increasing the ribothymidine content in a class C mammalian tRNA becomes manifest in an increased apparent maximum velocity for the overall synthesis of poly(Phe), while the apparent Michaelis constant (Km) remains essentially unchanged. It is postulated that the modified nucleoside ribothymidine might be involved in the regulation of protein synthesis at the level of translation in mammalian liver.

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