Hagervall T G, Björk G R
Mol Gen Genet. 1984;196(2):194-200. doi: 10.1007/BF00328050.
Two mutants of Escherichia coli, trmC1 and trmC2, which are both defective in the synthesis of 5-methylaminomethyl-2-thiouridine (mnm5s2U) were utilized to study the function of this complex modified nucleoside. Transfer RNAs specific for glutamine, glutamic acid and lysine as well as a specific ochre suppressor derived from lysine tRNA (tRNAUAAlys encoded by the supG allele), contain this modified nucleoside at position 34 (the wobble position). It was found that two different undermodified derivatives of mnm5s2U were present in the two trmC mutants, which suggests that the two mutations affect two different enzymatic activities. Using the lacI-Z fusion system (Miller and Albertini 1983), we found that the efficiency of supG-mediated suppression was reduced to 30%-90% of the wild-type value in the trmC mutants. The modification-deficient supG-tRNA in the mutants showed a higher sensitivity to codon context than the normal tRNAUAAlys.
利用大肠杆菌的两个突变体trmC1和trmC2来研究这种复杂修饰核苷的功能，这两个突变体在5-甲基氨甲基-2-硫代尿苷（mnm5s2U）的合成上均存在缺陷。谷氨酰胺、谷氨酸和赖氨酸特异性的转运RNA，以及源自赖氨酸tRNA的一种特异性赭石型抑制子（由supG等位基因编码的tRNAUAAlys），在第34位（摆动位置）含有这种修饰核苷。结果发现，两个trmC突变体中存在两种不同的mnm5s2U不完全修饰衍生物，这表明这两个突变影响两种不同的酶活性。使用lacI-Z融合系统（Miller和Albertini，1983），我们发现supG介导的抑制效率在trmC突变体中降至野生型值的30%-90%。突变体中缺乏修饰的supG-tRNA比正常的tRNAUAAlys对密码子上下文更敏感。
