Coleman R D, Dunst R W, Hill C W
Mol Gen Genet. 1980 Jan;177(2):213-22. doi: 10.1007/BF00267432.
The glyUsuAGA mutation affects Escherichia coli tRNA Gl y GGG, changing it to an AGA missense suppressor tRNA. Sequence studies have shown that the mutation involves a double base subsitution at the first and third positions of the tRNA anticodon, the result being a change in the anticodon from CCC to UCU. A system has been developed to facilitate the detection of this novel mutation, and we have shown that ultraviolet irradiation and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) are effective in causing the double base change. A single observation of the mutation occurring spontaneously has been made also. The frequency of MNNG-induced glyUsuAGA mutations is compatible with their being caused by two separate mutagenic events. The frequency of UV-induced glyAGA mutations, however, strongly suggests that the occurrence of one base substitution strongly enhances the chance of finding the second substitution at the alternate position. In addition to the double change in the anticodon, the glyUsuAGA tRNA differs from tRNA Gl y GGG in that it bears a modification of the A adjacent to the 3' position of the anticodon. Most likely, this modified base is N-[9-(beta-D-ribofuranosyl)-purin-6-ylcarbamoyl] threonine.
甘氨酸密码子AGA突变影响大肠杆菌的tRNA^Gly^GGG，使其转变为一种AGA错义抑制tRNA。序列研究表明，该突变涉及tRNA反密码子第一和第三位的双碱基替换，结果是反密码子从CCC变为UCU。已经开发出一种系统来促进对这种新突变的检测，并且我们已经表明紫外线照射和N-甲基-N'-硝基-N-亚硝基胍（MNNG）能有效地导致这种双碱基变化。也有一次自发发生该突变的观察记录。MNNG诱导的甘氨酸密码子AGA突变频率与其由两个独立的诱变事件引起相一致。然而，紫外线诱导的甘氨酸密码子AGA突变频率强烈表明，一个碱基替换的发生极大地增加了在另一个位置找到第二个替换的机会。除了反密码子的双碱基变化外，甘氨酸密码子AGA tRNA与tRNA^Gly^GGG的不同之处在于它在反密码子3'位置相邻的A上带有一个修饰。最有可能的是，这个修饰碱基是N-[9-(β-D-呋喃核糖基)-嘌呤-6-基氨基甲酰基]苏氨酸。
