Department of Molecular Biology, School of Biological Sciences, Centre for Advanced Studies in Functional and Organismal Genomics, Madurai Kamaraj University (University with Potential for Excellence), Madurai, India.
J Basic Microbiol. 2018 Jun;58(6):475-491. doi: 10.1002/jobm.201700645. Epub 2018 Apr 16.
As of date the two temperature sensitive mutations isolated in pheST operon include pheS5 (G →A ) and pheT354. Recently, we reported that G of pheS defines a hot spot for intragenic suppressors of pheS5. In this investigation, in 13 independent experiments, a collection of temperature sensitive mutants were isolated by localized mutagenesis. Complementation using clones bearing pheS , pheT , and pheS T indicated that 34 mutants could harbor lesion(s) in pheS and four could be in pheT and one mutant might be a double mutant. Surprisingly, all the 34 pheS mutants harbored the very same (G →A ) transition mutation as present in the classical pheS5 mutant. Most unexpectedly, the four pheT mutants isolated harbored the same G →A transition, a mutation which is hitherto unreported. Since all the four pheT mutants were defined by the same G →A base change, we believe that getting other mutations could be hard hitting and therefore it is proposed that G itself could be a "hot spot" for emergence of Ts mutations in pheT and similarly G itself could be a "hot spot" for Ts lesions in pheS. These results clearly imply a vital role for Glutamic acid (Glu ) of PheT and reinforce criticality of Glycine (Gly ) of PheS in the thermal stability of PheRS enzyme.
截至目前，pheST 操纵子中分离出的两个温度敏感突变包括 pheS5（G→A）和 pheT354。最近，我们报道 pheS 的 G 是 pheS5 基因内抑制子的热点。在这项研究中，通过局部位点诱变，在 13 个独立实验中分离了一组温度敏感突变体。使用携带 pheS、pheT 和 pheS T 的克隆进行互补表明，34 个突变体可能在 pheS 中有损伤，4 个可能在 pheT 中有损伤，1 个可能是双突变体。令人惊讶的是，所有 34 个 pheS 突变体都携带与经典 pheS5 突变体相同的（G→A）转换突变。最令人惊讶的是，分离出的 4 个 pheT 突变体都携带相同的 G→A 转换突变，这是迄今为止尚未报道的突变。由于所有 4 个 pheT 突变体都是由相同的 G→A 碱基变化定义的，我们相信获得其他突变可能是困难的，因此我们提出 G 本身可能是 pheT 中 Ts 突变出现的“热点”，类似地 G 本身可能是 pheS 中 Ts 损伤的“热点”。这些结果清楚地表明 PheT 的谷氨酸（Glu）和 PheS 的甘氨酸（Gly）在 PheRS 酶的热稳定性中起着至关重要的作用。
