Mangroo D, Limbach P A, McCloskey J A, RajBhandary U L
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA.
J Bacteriol. 1995 May;177(10):2858-62. doi: 10.1128/jb.177.10.2858-2862.1995.
Initiator tRNAs from eubacteria and chloroplasts lack a base modification next to the anticodon. This is in contrast to virtually all other tRNAs from these sources. We show that a mutant Escherichia coli initiator tRNA which has an anticodon sequence change from CAU to CUA now has a 2-methylthio-N6-(delta 2-isopentenyl)adenosine (ms2i6A) modification, produced by posttranscriptional modification of A, next to the anticodon. This newly acquired base modification may be important for the function of the mutant tRNA in initiation. In a miaA mutant strain of E. coli defective in biosynthesis of ms2i6A, the mutant initiator tRNA is 10- to 12-fold less active in initiation. The mutant tRNA is aminoacylated and formylated normally in the miaA strain. Thus, the absence of the base modification affects the activity of the mutant tRNA at a step subsequent to its formylation.
真细菌和叶绿体中的起始tRNA在反密码子旁边缺少碱基修饰。这与这些来源的几乎所有其他tRNA形成对比。我们发现，一种反密码子序列从CAU变为CUA的突变型大肠杆菌起始tRNA，现在在反密码子旁边有一个由A的转录后修饰产生的2-甲硫基-N6-（δ2-异戊烯基）腺苷（ms2i6A）修饰。这种新获得的碱基修饰可能对突变tRNA在起始过程中的功能很重要。在ms2i6A生物合成有缺陷的大肠杆菌miaA突变株中，突变起始tRNA的起始活性降低了10至12倍。突变tRNA在miaA菌株中正常进行氨酰化和甲酰化。因此，碱基修饰的缺失在突变tRNA甲酰化后的一个步骤影响其活性。
