Phillips Gabriella, El Yacoubi Basma, Lyons Benjamin, Alvarez Sophie, Iwata-Reuyl Dirk, de Crécy-Lagard Valérie
Department of Microbiology, University of Florida, Gainesville, FL 32611-0700, USA.
J Bacteriol. 2008 Dec;190(24):7876-84. doi: 10.1128/JB.00874-08. Epub 2008 Oct 17.
Queuosine (Q) and archaeosine (G(+)) are hypermodified ribonucleosides found in tRNA. Q is present in the anticodon region of tRNA(GUN) in Eukarya and Bacteria, while G(+) is found at position 15 in the D-loop of archaeal tRNA. Prokaryotes produce these 7-deazaguanosine derivatives de novo from GTP through the 7-cyano-7-deazaguanine (pre-Q(0)) intermediate, but mammals import the free base, queuine, obtained from the diet or the intestinal flora. By combining the results of comparative genomic analysis with those of genetic studies, we show that the first enzyme of the folate pathway, GTP cyclohydrolase I (GCYH-I), encoded in Escherichia coli by folE, is also the first enzyme of pre-Q(0) biosynthesis in both prokaryotic kingdoms. Indeed, tRNA extracted from an E. coli DeltafolE strain is devoid of Q and the deficiency is complemented by expressing GCYH-I-encoding genes from different bacterial or archaeal origins. In a similar fashion, tRNA extracted from a Haloferax volcanii strain carrying a deletion of the GCYH-I-encoding gene contains only traces of G(+). These results link the production of a tRNA-modified base to primary metabolism and further clarify the biosynthetic pathway for these complex modified nucleosides.
Queuosine (Q)和archaeosine (G(+))是在tRNA中发现的高度修饰的核糖核苷。Q存在于真核生物和细菌中tRNA(GUN)的反密码子区域，而G(+)则存在于古细菌tRNA D环的第15位。原核生物通过7-氰基-7-脱氮鸟嘌呤（前Q(0)）中间体从GTP从头合成这些7-脱氮鸟苷衍生物，但哺乳动物摄入从饮食或肠道菌群中获得的游离碱基queuine。通过将比较基因组分析结果与遗传研究结果相结合，我们表明，在大肠杆菌中由folE编码的叶酸途径的第一种酶，即GTP环化水解酶I (GCYH-I)，也是两个原核生物界中前Q(0)生物合成的第一种酶。事实上，从大肠杆菌DeltafolE菌株中提取的tRNA不含Q，通过表达来自不同细菌或古细菌来源的GCYH-I编码基因可以弥补这种缺陷。以类似的方式，从携带GCYH-I编码基因缺失的嗜盐栖热菌菌株中提取的tRNA仅含有微量的G(+)。这些结果将tRNA修饰碱基的产生与初级代谢联系起来，并进一步阐明了这些复杂修饰核苷的生物合成途径。
