Effect of modified bases on the three-dimensional structure and physiological activities of yeast tyrosine tRNA.

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Originally, it was planned that two types of chimeric tRNA (T5N3, N5T3) were synthesized by exchanged re-union of 5’-and 3’-half fragments obtained through limited digestion of yeast tRNA^Tyr and tRNA^Tyr transcript and used for the analyses on the relationship between the modified base-content and the stability of three-dimensional structure of tRNA. However, it was turned out to be difficult by technical reasons. Therefore, similar experiments were performed by using the anticodon nuclease VapC which was recently developed in our laboratory and E. colitRNA^Leu. The result of Tm-measurement showed that the heat-stability of tRNAs increased in the order of tRNA^Leu transcript＜T5N3＜N5T3＜native tRNA^Leu, indicating that the modified bases, especially those contained in the 5’-half fragment (N5) have the effectof stabilizing three-dimensional structure of tRNA. However, unexpected result was also obtained that the native form of tRNA^Leu is less stable than the transcript tRNA in the absence of Mg2+. It is interesting in a sense that the modified bases can contribute to both of the stability and instability of the higher-order structure of tRNA depending on the state of interaction with Mg2+.