Sroga G E, Nemoto F, Kuchino Y, Björk G R
Department of Microbiology, University of Umeå, Sweden.
Nucleic Acids Res. 1992 Jul 11;20(13):3463-9. doi: 10.1093/nar/20.13.3463.
The dominant +1 frameshift suppressors sufA6, sufB1 and sufB2, in Salmonella typhimurium act at runs of C and affect tRNA(Pro)1, tRNA(Pro)2 and tRNA(Pro)2, respectively. A recessive +1 frameshift suppressor, sufC, has a similar suppressor specificity (Riddle, D.L., and Roth, J.R., Mol. Biol. 66, 483 and 495, 1972). We show that sufC strains harbour two frameshift suppressors of which one, sufX201, is allelic to sufB. We cloned the sufB+ wild type allele and by recombination in vivo the mutations sufB1, sufB2 and sufX201. Determination of the DNA sequence revealed that the sufB1 and sufB2 mutations result in an extra G in the anticodon loop of the minor tRNA(Pro)2. The sufX201 mutation results in a base substitution (G43 to A43) in the anticodon stem of this tRNA. Although the sufB1 and sufB2 mutations were earlier shown to be dominant, the sufB+ wild type allele on multi copy plasmid inhibited the chromosomal sufB1, sufB2 and sufX201 mediated frameshift suppression but not that mediated by the dominant sufA6 mutation. These results are discussed in view of the possible coding specificity of these mutated tRNAs. The DNA sequence showed a potential consensus promoter sequence upstream of the structural gene for tRNA(Pro)2 and downstream a dyad symmetrical structure followed by a T cluster, a possible rho-independent termination signal. The Salmonella tRNA(Pro)2 gene is identical to the Escherichia coli counterpart reported by Komine, Y. et al. (J. Mol. Biol. 212, 579-598, 1990). While the 5' flanking sequence similarity between the two species is about 83%, the similarity of the 3' flanking sequence is only 42%. Still, the Salmonella tRNA(Pro)2 gene has a rho-independent transcriptional termination signal similar to the one present in E. coli tRNA(Pro)2 gene.
鼠伤寒沙门氏菌中占主导地位的 +1 移码抑制因子 sufA6、sufB1 和 sufB2 分别作用于 C 碱基连续出现的区域，并分别影响 tRNA(Pro)1、tRNA(Pro)2 和 tRNA(Pro)2。一个隐性 +1 移码抑制因子 sufC 具有相似的抑制特异性（里德尔，D.L.，和罗斯，J.R.，《分子生物学》66 卷，483 页和 495 页，1972 年）。我们发现 sufC 菌株含有两个移码抑制因子，其中一个，sufX201，与 sufB 等位。我们克隆了 sufB+ 野生型等位基因，并通过体内重组得到了 sufB1、sufB2 和 sufX201 突变体。DNA 序列测定表明，sufB1 和 sufB2 突变导致次要的 tRNA(Pro)2 的反密码子环中额外出现一个 G。sufX201 突变导致该 tRNA 的反密码子茎中发生碱基替换（G43 变为 A43）。尽管 sufB1 和 sufB2 突变先前被证明是显性的，但多拷贝质粒上的 sufB+ 野生型等位基因抑制了染色体上 sufB1、sufB2 和 sufX201 介导的移码抑制，但不抑制由显性的 sufA6 突变介导的移码抑制。鉴于这些突变 tRNA 可能的编码特异性，对这些结果进行了讨论。DNA 序列显示，在 tRNA(Pro)2 的结构基因上游有一个潜在的共有启动子序列，下游有一个二元对称结构，接着是一个 T 簇，这可能是一个不依赖 ρ 因子的终止信号。沙门氏菌的 tRNA(Pro)2 基因与小宫义彦等人报道的大肠杆菌对应基因相同（《分子生物学杂志》212 卷，579 - 598 页，1990 年）。虽然这两个物种 5' 侧翼序列的相似性约为 83%，但 3' 侧翼序列的相似性仅为 42%。不过，沙门氏菌的 tRNA(Pro)2 基因有一个类似于大肠杆菌 tRNA(Pro)2 基因中存在的不依赖 ρ 因子的转录终止信号。
