Functional Role of Ribosylthymine in Transfer RNA

Abstract

In some eucaryotes tRNA species occur containing exclusively uridine or ribosylthymine at position 54. In other eucaryotic tRNA species varying ratios of uridine to ribosylthymine have been found. To elucidate whether variation in the degree of U54 methylation in eucaryotic tRNA plays a functional role in protein synthesis, polysomal and overal cellular tRNAs in the lower eucaryote Dictyostelium discoideum were characterized during vegetative growth and the early developmental preaggregation stage.The nucleoside composition of the tRNAs was determined and U54-containing tRNA species were detected after methylation in vitro with the rT-forming enzyme from Escherichia coli. The following results were obtained. The results demonstrate that in D. discoideum, the major class tRNAs utilized for protein synthesis includes molecular species in which a Us4 residue has been methylated to rT. The ratio of rTs4 to Us4 in these tRNAs declines at a physiological stage at which the rate of protein synthesis is reduced. Since in vitro an eucaryotic U54-containing tRNA of this class translates mRNA less efficiently than its rT-containing counterpart [K. B. Marcu and B. S. Dudock (1976) Nature (Lond.) 261, 159-1621, it is assumed that these W4-containing tRNAs are rate-limiting in the elongation of peptide chains in eucaryotes.

Proteins and Nucleic Acids in Plant Systematics

“…Similarly the presence of the modified base Q in the anticodon of several mammalian tRNAs is related to the cell differentiation (Dingermann et al 1981) and is also found to be different in normal and cancer cells (Okada et al 1978, Shindo-Okada et al 1981. Similar experiments with intact tRNA species, modified on the residue-54 to different extents, provide similar results (Dingermann et al 1980. Sprinzl and Gauss (1982).…”

Polyacrylamide Gel Mapping of Chicken tRNA: Comparison of Polysome-Bound and Whole-Cell tRNA from Normal and Avian Sarcoma Virus-Infected Chicken Embryo Fibroblasts

“…Modified bases located adjacent to the anticodon were shown to enhance the codon-anticodon interaction (22). Moreover, it has been shown that tRNAs containing ribosyithymidine at position 54 predominate on polysomes (3) and are more efficient for in vitro protein synthesis than their U54-containing counterparts (26). However, this possible selection cannot account alone for the observed differences in the tRNA distribution between whole-cell and polysomal preparations, as some amino acid-specific tRNA groups were found in quite different proportions in both preparations.…”

Regulation of tRNA methyltransferase activities by spermidine and putrescine. Inhibition of polyamine synthesis and tRNA methylation by α-methylornithine or 1,3-diaminopropan-2-ol in Dictyostelium discoideum

“…The nucleic acids were precipitated from the aqueous phase with 2.5vol. of ethanol, dissolved in electrophoresis buffer and applied to electrophoresis on a 10% polyacrylamide gel (Dingermann et al, 1980).…”