State Key Laboratory for Agrobiotechnology and College of Biological Sciences, China Agricultural University, Beijing 100094, China.
Int J Mol Sci. 2021 Mar 16;22(6):3033. doi: 10.3390/ijms22063033.
Serine is important for nearly all microorganisms in protein and downstream amino acids synthesis, however, the effect of serine on growth and nitrogen fixation was not completely clear in many bacteria, besides, the regulatory mode of serine remains to be fully established. In this study, we demonstrated that L-serine is essential for growth and nitrogen fixation of WLY78, but high concentrations of L-serine inhibit growth, nitrogenase activity, and expression. Then, we revealed that expression of the whose gene product catalyzes the first reaction in the serine biosynthetic pathway is regulated by the T-box riboswitch regulatory system. The 508 bp mRNA leader region upstream of the coding region contains a 280 bp T-box riboswitch. The secondary structure of the T-box riboswitch with several conserved features: three stem-loop structures, a 14-bp T-box sequence, and an intrinsic transcriptional terminator, is predicted. Mutation and the transcriptional leader- fusions experiments revealed that the specifier codon of serine is AGC (complementary to the anticodon sequence of tRNA). qRT-PCR showed that transcription of is induced by serine starvation, whereas deletion of the specifier codon resulted in nearly no expression of . Deletion of the terminator sequence or mutation of the continuous seven T following the terminator led to constitutive expression of . The data indicated that the T-box riboswitch, a noncoding RNA segment in the leader region, regulates expression of by a transcription antitermination mechanism.
丝氨酸对几乎所有微生物的蛋白质和下游氨基酸合成都很重要，然而，在许多细菌中，丝氨酸对生长和固氮的影响并不完全清楚，此外，丝氨酸的调控模式仍有待充分建立。在本研究中，我们证明 L-丝氨酸对 WLY78 的生长和固氮是必不可少的，但高浓度的 L-丝氨酸会抑制生长、固氮酶活性和表达。然后，我们揭示了编码丝氨酸生物合成途径中第一个反应的酶的基因产物的表达受 T 框核糖体开关调控系统的调节。 编码区上游的 508bp mRNA 前导区包含一个 280bp 的 T 框核糖体开关。T 框核糖体开关的二级结构具有几个保守特征：三个茎环结构、一个 14bp 的 T 框序列和一个内在转录终止子，可预测。突变和转录前导融合实验表明，丝氨酸的特异性密码子是 AGC（与 tRNA 的反密码子序列互补）。qRT-PCR 显示，在丝氨酸饥饿时， 转录被诱导，而特异性密码子的缺失导致几乎没有 的表达。终止子序列的缺失或连续七个 T 后的突变导致 的组成型表达。数据表明，非编码 RNA 片段在启动子区域的 T 框核糖体开关通过转录终止机制调节 的表达。
