Cell-free enzymic esterification of 5-carboxymethyluridine residues in bulk yeast transfer RNA

Presence of the methylester of 5-carboxymethyl uridine in the wobble position of the anticodon of tRNAIII Arg from brewer's yeast

The methylester of 5-carboxymethyluridine (mcm5U), its degradation product 5-carboxymethyluridine (cm5U) and the corresponding nucleotide (cm5Up) were isolated from brewer's yeast tRNAIII Arg or from the dodecanucleotide containing the anticodon. Their chromatographic and electrophoretic properties and their UV absorbing spectra were identical to that of the corresponding synthetic compounds. The gas chromatographic behavior and the mass spectrum of mcm5U obtained from tRNAIII Arg and of a synthetic sample were also identical ; the rare occurence of a thermal reciprocal bimolecular methyl-hydrogen transfer in the mass spectrometer ion source was observed. A mild alkaline treatment of tRNAIII Arg leads to the saponification of mcm5U into cm5U (within the tRNA), which can be again esterified in the presence of a yeast homogenate and (methyl-14C) S adenosylmethionine. The radioactivity was found in the mcm5U located in the wobble position of the anticodon of tRNAIII Arg. The presence of this odd nucleotide in that position could possibly restrict the codon-anticodon interaction of tRNAIII Arg.

Transfer RNA methyltransferases from yellow lupin seeds: purification and properties

tRNA methyltransferases from extract of yellow lupin seeds were purified over 300-fold by the methods based on hydrophobic and affinity chromatography. However, in the most active fractions the methylating enzymes were over 2000 purified. The purified enzyme fractions catalysed the formation of 1-methyladenine and 5-methylcytosine using E. coli B and B. subtilis tRNAs as substrates and S-adenosylmethionine as the methyl donor. They were unable to methylate their own endogenous tRNA but they were capable of methylating tRNA of some other lupinus species. Whereas the patterns of methylated constituents of tRNA of some other lupinus and B. subtilis were quite similar, they differed considerably from those obtained with lupin species tRNAs. Some properties of purified methyltransferases from yellow lupin seeds have been described.