Identification and characterization of tRNA (Gm18) methyltransferase from Thermus thermophilus HB8: domain structure and conserved amino acid sequence motifs.
BACKGROUND
Transfer RNAs from an extreme thermophile, Thermus thermophilus, commonly possess 2'-O-methylguanosine at position 18 (Gm18) in the D-loop. This modification is post-transcriptionally introduced by tRNA (Gm18) methyltransferase.


RESULTS
Partial amino acid sequence data were obtained from purified T. thermophilus tRNA (Gm18) methyltransferase by peptide sequencing and mass spectrometry. The sequence data were used to screen the T. thermophilus genome database currently in progress, resulting in the identification of the corresponding gene. Purified recombinant enzyme showed a strict specificity for methylation at the 2'-OH of G18 in tRNA. Sequence alignment with other known or putative methyltransferases elucidates that tRNA (Gm18) methyltransferases have specific conserved region as well as three consensus motifs found in RNA ribose 2'-O-methyltransferases. The enzyme truncated at its N and C termini by limited tryptic digestion still retained binding activity for S-adenosyl-l-homocysteine, but lost the catalytic activity.


CONCLUSIONS
This is the first report describing the identification of a methyltransferase gene of the trmH family through the analysis of a purified protein. Further, our results indicate that a restricted region(s) in the terminal amino acid residues of T. thermophilus tRNA (Gm18) methyltransferase are responsible for tRNA recognition and a main part of the enzyme is allocated for a catalytic core.
Hori
Hiroyuki
H
Department of Biochemistry and Molecular Biology, Nippon Medical School, Bunkyo-ku, Tokyo 113-8602, Japan.
Suzuki
Tsutomu
T
Sugawara
Kazumasa
K
Inoue
Yorinao
Y
Shibata
Takehiko
T
Kuramitsu
Seiki
S
Yokoyama
Shigeyuki
S
Oshima
Tairo
T
Watanabe
Kimitsuna
K
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D017124:Conserved Sequence; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D016963:Thermus thermophilus / Q000201:enzymology* / Q000235:genetics; D012359:tRNA Methyltransferases / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D012359:tRNA Methyltransferases