Effect of cations on tRNA structure

Bolton, P.H.; Kearns, D.R.

Biochemistry 16(26): 5729-5741

1977


ISSN/ISBN: 0006-2960
PMID: 338029
DOI: 10.1021/bi00645a013
Accession: 068526569

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Abstract
The structure of tRNA in the presence of certain cations was investigated by high-resolution NMR. In the presence of 0.17 M Na at 22.degree. C the structure of tRNA is similar to, but no identical with, the native structure. At higher temperatures the difference between the native structure and the structure in the presence of 0.17 M Na increases. Mg sequentially stabilizes the tRNA structure in the presence of 0.17 M Na in the temperature range 22-44.degree. C, the number of Mg required for the stabilization of the native structure increases from 2 .+-. 1 at 22.degree. C to 4 .+-. 1 at 44.degree. C, and the number of interactions with slowly exchanging H-bonded imino protons stabilized increases from 1 .+-. 1 at 22.degree. C to 4 .+-. 1 at 44.degree. C. The polyamines spermine and spermidine stabilize some, but not all, of the interactions stabilized by Mg. For tRNA in the presence of 0.17 M Na at 44.degree. C, 3-4 spermine per tRNA stabilizes 2 .+-. 1 interactions with slowly exchanging H-bonded imino protons. The combination of spermine and Mg was more effective than either cation alone in stabilizing the native structure of tRNA. The NMR results offer no evidence that the structure of tRNA in the presence of both spermine and Mg (at high levels of both cations) is different from the native structure. In the presence of tetraethylammonium or tetramethylammonium ions, the tRNA structure is extensively destabilized relative to the native structure. Addition of Mg to such samples stabilizes the native structure in a nonsequential manner, and about 8 Mg per tRNA are needed for the stabilization. The NMR results are taken in conjunction with the results of other investigators to propose a comprehensive model for the interaction of tRNA with cations. The use of assignments of some resonances to specific tertiary interactions suggests that Mg stabilizes the tertiary interactions of tRNA in the following order: s4U8 .cntdot. A14, U33, A58 .cntdot. T54 and G19 .cntdot. C56.