A thermostable Gm-methylase recognizes the tertiary structure of tRNA.
The efficiency of methylation of tRNA by a thermostable tRNA(guanosine-2')-methyltransferase (Gm-methylase) was examined at various temperatures using several species of tRNA isolated from Escherichia coli, yeast and Bacillus subtilis, each possessing different thermal properties. The optimal temperature for the methylation reaction was ca. 20 degrees C lower than the melting temperature of the tRNA in each case. Arrhenius plots of the methylation reactions with various tRNAs gave straight lines below the optimal temperatures in all cases, with similar activation energies of between 10 and 14 kcal/mol. Above the optimal temperatures, the methyl acceptor activity decreased as the incubation temperature was raised to 80 degrees C, at which point the methylase was still active. A correlation was observed between the remaining methyl acceptor activity and the hyperchromicity of tRNA. These results suggest that Gm-methylase recognizes the tertiary structure of tRNA, and it is not the substrate tRNA but the enzyme which is activated by heat.
Matsumoto
T
T
Department of Agricultural Chemistry, Faculty of Agriculture, University of Tokyo, Japan.
Ohta
T
T
Kumagai
I
I
Oshima
T
T
Murao
K
K
Hasegawa
T
T
Ishikura
H
H
Watanabe
K
K
D001483:Base Sequence; D004795:Enzyme Stability; D004926:Escherichia coli; D006358:Hot Temperature; D007700:Kinetics; D046911:Macromolecular Substances; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D012343:RNA, Transfer / Q000378:metabolism*; D012441:Saccharomyces cerevisiae; D013816:Thermodynamics; D012359:tRNA Methyltransferases / Q000378:metabolism*
D046911:Macromolecular Substances; D012343:RNA, Transfer; D012359:tRNA Methyltransferases; C023196:tRNA (guanine(10)-N(2))-dimethyltransferase