Studies on thionucleotides in the transfer ribonucleic acids of agrobacterium tumefaciens and corynebacterium fascians

Abstract

A fast and simple paper electrophoretic method for the separation and identification of thionucleotides in tRNA was developed and it was applied for investigating the sulphur-containing nucleotides in the tRNA from Agrobacterium tumefaciens and Corynebacterium fascians. Six major thiolated species were detected in the former and four from the latter. In both the organisms, 2-methylthioribosylzeatin monophosphate (ms io Ap) was found to be the predominant thionucleotide. In C.fascians, a new thionucleotide, ’X p ’, was partially identified as a 2-thiouridine derivative, probably ; containing a carboxylic acid group. Separation of 55S-labelled tRNA into two peaks, one containing 2-methyl- ? f\ thioribosylzeatin (ms io A) and the other containing 5-methylaininomethyl-2- thiouridine (mam^s^U), was effected by column chromatographic procedures. From a study of the nucleotide composition of the anticodon loop regions of tRNAs containing sulphur, and comparing them with the reported sequences of several tRNAs, the major tRNA species containing ms io Ap in C.fascians were found to be tRNA e and tRNA . Presence of both ms io Ap and 'Xp' was observed in one of the serine-tRNAs. A study on the variation' of thionucleotides under different culture conditions of temperature and period of growth, showed a precursor-product relationship between 2-thiouridylate ( s ^ p ) and 5-methylaminomethyl-2-thio- uridylate (mam^s^p) on the one hand, and between ms2i Ap and ms io Ap on the other. From these. studies, a tentative pathway for the biosynthesis of the hypermodified thionucleotide, mam^s has been proposed as: Up ------ a,- s^U p — r- T a ^ s ^ p — ^ --- * mam^s2Up These studies have also suggested that the modified nucleotides in c general have control functions in cellular metabolism.