A novel enzymatic pathway leading to 1-methylinosine modification in Haloferax volcanii tRNA.
Transfer RNAs of the extreme halophile Haloferax volcanii contain several modified nucleosides, among them 1-methylpseudouridine (m1 psi), pseudouridine (psi), 2'-0-methylcytosine (Cm) and 1-methylinosine (m1l), present in positions 54, 55, 56 and 57 of the psi-loop, respectively. At the same positions in tRNAs from eubacteria and eukaryotes, ribothymidine (T-54), pseudouridine (psi-55), non-modified cytosine (C-56) and non-modified adenosine or guanosine (A-57 or G-57) are found in the so-called T psi-loop. Using as substrate a T7 transcript of Haloferax volcanii tRNA(Ile) devoid of modified nucleosides, the enzymatic activities of several tRNA modification enzymes, including those for m1 psi-54, psi-55, Cm-56 and m1l-57, were detected in cell extracts of H.volcanii. Here, we demonstrate that modification of A-57 into m1l-57 in H.volcanii tRNA(Ile) occurs via a two-step enzymatic process. The first step corresponds to the formation of m1A-57 catalyzed by a S-adenosylmethionine-dependent tRNA methyltransferase, followed by the deamination of the 6-amino group of the adenine moiety by a 1-methyladenosine-57 deaminase. This enzymatic pathway differs from that leading to the formation of m1l-37 in the anticodon loop of eukaryotic tRNA(Ala). In the latter case, inosine-37 formation preceeds the S-adenosylmethionine-dependent methylation of l-37 into m1l-37. Thus, enzymatic strategies for catalyzing the formation of 1-methylinosine in tRNAs differ in organisms from distinct evolutionary kingdoms.
Grosjean
H
H
Laboratoire d'Enzymologie et de Biochimie Structurales, CNRS, Gif-sur-Yvette, France.
Constantinesco
F
F
Foiret
D
D
Benachenhou
N
N
D000241:Adenosine / Q000031:analogs & derivatives* / Q000378:metabolism; D001483:Base Sequence; D006216:Halobacteriaceae / Q000201:enzymology*; D007288:Inosine / Q000031:analogs & derivatives* / Q000096:biosynthesis; D008969:Molecular Sequence Data; D009705:Nucleosides / Q000032:analysis; D011560:Pseudouridine / Q000096:biosynthesis; D012323:RNA Processing, Post-Transcriptional; D012329:RNA, Bacterial / Q000378:metabolism; D012355:RNA, Transfer, Ile / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
D009705:Nucleosides; D012329:RNA, Bacterial; D012355:RNA, Transfer, Ile; D011560:Pseudouridine; C002230:1-methyladenosine; C012433:1-methylinosine; D007288:Inosine; D000241:Adenosine