Girish B. Chheda

Cytokinin Activity of Ureidopurine Derivatives Related to a Modified Nucleoside Found in Transfer RNA

By use of a radioactive labeling technique N-(nebularin-6-ylcarbamoyl)threonine has been detected in plant transfer RNA. Derivatives of this nucleoside promote cell division of a cytokinin-requiring soya bean tissue.

Interaction of the tRNA-derived unusual nucleoside, tp6A, with Mn(II) and Mg(II)

We have been interested for some time in the role certain unusual anticodon-adjacent nucleosides might play in the structure and functions of transfer RNA. One of these,N-[9-(/3-D-ribofuranosyl) purindylcarbamoyllthreonine, t6A ([ 1,2], fig.1) occurs at the 3’end of the anticodon in most tRNAs which read codons beginning with adenosine 131. We have shown in [4] that t6A is required for optimal interaction of Escherichia coli Be-tRNA% with poly(AUC) on ribosomes. t6A-deficient tRNA bound less extensively as a function of Mg(II), suggesting that the modified nucleoside could be serving as a metal ligand. We have also presented [5] qualitative evidence for the interaction of Mn(I1) with t6A by 13C NMR. The paramagnetic Mn(I1) ion was shown to bind primarily to the carboxyl group, with other possible coordination sites being N, and Nr of the adenine ring and the ureido carbonyl oxygen of the sidechain. Though Mn(II)is considered in most instances a good substitute for Mg(I1) in terms of biological activity and ionic size, it was thought important to investigate the interaction of Mg(I1) with t6A directly by other techniques. Here we report a study on the interaction of Mg(I1) with t6A using potentiometry. We have also studied the Mn(II)interaction with this ligand for comparison.