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Nucleic Acids Research, 1983, Vol. 11, No. 12 4257-4272
© 1983

ENZYMOLOGY

The role of queuine in the aminoacylation of mammalian aspartate transfer RNAs

Ram P. Singhal*,+ and Vikram N. Vakharia+

*Laboratory of Cellular and Molecular Biology, Gerontology Research Center NLA, NIH, Baltimore, MD 21224 +Department of Chemistry, Wichita State University Wichita, KS 67208, USA

Received March 1, 1983. Revised April 26, 1983. Accepted May 24, 1983.

Can a queuine-specific tRNA function normally without replacement of G by Q in its structure? To answer this, kinetics of aspartate queuine-containing tRNA (Q-tRNA) is compared with its queuine-deficient counterpart (G-tRNA). The results indicate that Asp Q-tRNA is a more effective substrate than the Asp G-tRNA. The Asp Q-tRNA exhibits a higher reaction velocity (Vmax >30%) and a higher reaction rate (km <55%) than its counterpart. The Asp tRNAs derived from human tumor lines and grown in athymic mice contain a full complement of queuine. This tumor tRNA exhibits aminoacylation kinetics similar to a normal liver tRNA. Reasons for observing the lack of a G-to-Q modification in cancer tRNAs by others are hypothesized. Two purified Asp isoacceptors from liver are compared for the aminoacylation reaction; small differences are noted in the Vmax, but none in the Km values.


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