A NOVEL ENZYMATIC PATHWAY LEADING TO 1-METHYLINOSINE MODIFICATION IN HALOFERAX-VOLCANII TRANSFER-RNA
A NOVEL ENZYMATIC PATHWAY LEADING TO 1-METHYLINOSINE MODIFICATION IN HALOFERAX-VOLCANII TRANSFER-RNA
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DOI：
10.1093/nar/23.21.4312
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发表时间：
1995-11-11
影响因子：
14.9
通讯作者：
BENACHENHOU, N
中科院分区：
文献类型：
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作者：
GROSJEAN, H;CONSTANTINESCO, F;BENACHENHOU, N
极端嗜盐菌Haloferax Volcanii的转移RNA含有几个修饰的核苷，其中1-甲基假尿苷(m(1)psi)、伪尿苷(Psi)、2‘-O-甲基胞嘧啶(Psi)和1-甲基肌苷(m(1)I)分别存在于psi环的第54、55、56和57位，在所谓的T psi环中发现了胸苷(T-54)、伪尿苷(psi-55)、未修饰胞苷(C-56)和纳米修饰的腺苷或鸟苷(A-57或0-57)。以不含修饰核苷的盐藻tRNA(ILE)的T-7转录本为底物，检测了几种tRNA修饰酶的活性，包括m(1)psi-54、psi-55、cm-56和m(1)I-57的酶活性。在这里，我们证明了在H，Volcanii tRNA(ILE)中，A-57被修饰成m(1)I-57是通过两步酶过程进行的，第一步对应于S腺苷蛋氨酸依赖的tRNA甲基转移酶催化形成m(1)A-57随之而来的是腺嘌呤部分的6-氨基被1-甲基腺苷-57脱氨酶脱氨，这一酶途径与导致真核生物tRNA(ALA)反密码子环中m(1)I-37形成的酶途径不同，在后者的情况下，肌苷-37的形成先于依赖S-腺苷蛋氨酸的甲基化成m(1)I-37，因此，催化tRNA中1-甲基肌苷形成的酶策略在不同的进化王国中有所不同。
Transfer RNAs of the extreme halophile Haloferax volcanii contain several modified nucleosides, among them 1-methylpseudouridine (m(1) psi), pseudouridine (psi), 2'-O-methylcytosine (psi) and 1-methylinosine (m(1)I), 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 nan-modified adenosine or guanosine (A-57 or 0-57) are found in the so-called T psi-loop. Using as substrate a T-7 transcript of Haloferax volcanii tRNA(Ile) devoid of modified nucleosides, the enzymatic activities of several tRNA modification enzymes, including those for m(1) psi-54, psi-55, Cm-56 and m(1)I-57, were detected in cell extracts of H,volcanii, Here, we demonstrate that modification of A-57 into m(1)I-57 in H,volcanii tRNA(Ile) occurs via a two-step enzymatic process, The first step corresponds to the formation of m(1) A-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 m(1)I-37 in the anticodon loop of eukaryotic tRNA(Ala), In the latter case, inosine-37 formation preceeds the S-adenosylmethionine-dependent methylation of I-37 into m(1) I-37, Thus, enzymatic strategies for catalyzing the formation of 1-methylinosine in tRNAs differ in organisms from distinct evolutionary kingdoms.