Jänel G, Michelsen U, Nishimura S, Kersten H
EMBO J. 1984 Jul;3(7):1603-8. doi: 10.1002/j.1460-2075.1984.tb02017.x.
In eubacteria the modified nucleoside queuosine is present in tRNAAsn, tRNAAsp, tRNAHis and tRNATyr. A precursor of queuine, pre-queuine, is synthesized from GTP, inserted into the first position of the anticodon of the corresponding tRNAs by a specific tRNA-guanine transglycosylase and further modified to queuosine. Isogenic pairs of Escherichia coli, containing or lacking the tRNA-transglycosylase (JE 7335, tgt+ lacZ+ and JE 7337, tgt- lacZ+; JE 7334, tgt+ lacZ- and JE 7336, tgt- lacZ-), have been employed to study the function of queuosine in tRNA. Compared with the tgt+ strain (JE 7335), the tgt- mutant (JE 7337) grown under anaerobic conditions, is defective with respect to the nitrate respiration system, in which electrons are transported from D(-)-lactate via quinone and cytochrome bNO3-(556) to nitrate. Low temperature cytochrome spectra of the anaerobically grown tgt- mutant show a lowered amount of type b cytochromes involving the spectrum of cytochrome bNO3-(556). In the case of the anaerobically grown tgt- mutant three proteins are missing in the protein pattern of cytoplasmic membranes. Their mol. wts. correspond to those of the subunits of the nitrate reductase complex. In contrast to the tgt+ strains (JE 7334, JE 7335) both tgt- mutants (JE 7336, JE 7337) cannot grow on lactate under anaerobic conditions with nitrate offered as electron acceptor and NO3- is not reduced to NO2-. A possible link between Q-modification of tRNAs, the synthesis of proteins of the nitrate reductase complex and the synthesis of menaquinone or ubiquinone is discussed.
在真细菌中，修饰核苷queuosine存在于tRNAAsn、tRNAAsp、tRNAHis和tRNATyr中。queuine的前体，即前queuine，由GTP合成，通过特定的tRNA-鸟嘌呤转糖基酶插入到相应tRNA反密码子的第一位，然后进一步修饰为queuosine。含有或缺乏tRNA转糖基酶的大肠杆菌同基因对（JE 7335，tgt+ lacZ+和JE 7337，tgt- lacZ+；JE 7334，tgt+ lacZ-和JE 7336，tgt- lacZ-）已被用于研究queuosine在tRNA中的功能。与tgt+菌株（JE 7335）相比，在厌氧条件下生长的tgt-突变体（JE 7337）在硝酸盐呼吸系统方面存在缺陷，在该系统中，电子从D(-)-乳酸经醌和细胞色素bNO3-(556)传递至硝酸盐。厌氧生长的tgt-突变体的低温细胞色素光谱显示，涉及细胞色素bNO3-(556)光谱的b型细胞色素数量减少。在厌氧生长的tgt-突变体的情况下，细胞质膜的蛋白质图谱中缺少三种蛋白质。它们的分子量与硝酸还原酶复合物亚基的分子量相对应。与tgt+菌株（JE 7334、JE 7335）相反，两个tgt-突变体（JE 7336、JE 7337）在以硝酸盐作为电子受体的厌氧条件下不能利用乳酸生长，并且NO3-不会被还原为NO2-。文中讨论了tRNA的Q修饰、硝酸还原酶复合物蛋白质的合成以及甲萘醌或泛醌的合成之间可能存在的联系。
