碳源與飢餓培養對大腸桿菌rne基因表現之影響

Abstract

mRNA穩定度是細胞中蛋白合成重要決定步驟。在大腸桿菌體內之RNase E是多數mRNA降解的速率決定步驟，另外對rRNA成熟、菌體中特殊polycistronic RNA選擇性切割以及DNA複製也需要RNase E參與，由此可知RNase E是菌體中不可缺少的酵素。 過去文獻指出，外在環境會影響RNase E受質結構，或藉由其他輔助因子調控使RNase E對受質親合力改變。然而其中，環境因子如何調控RNase E表現是我們有興趣探討的目標。 改變碳源、生長速率以及貧瘠培養以觀察外在營養源對rne基因的調控行為，結果發現碳源會參與調控rne m RNA穩定性，以葡萄糖為碳源時穩定度較高，且rne mRNA穩定度隨著生長速率增加而下降，其目的在嚴格調控菌體中RNase E濃度，以維持正常生理平衡。 此外迫切反應是調控細胞生長速率的兩大系統之一，在貧瘠培養中發現rne mRNA快速降解，且rne啟動子不具表現活性。另外，飢餓反應藉由(p)ppGpp快速大量水解RNase E，這些反應可減緩菌體中多數mRNA的降解速率，以在環境許可時快速回復正常生理狀態。

Post-transcriptional regulation is an important mechanism for controlling gene expression. RNase E, encoded by the rne gene, is a key enzyme that decides the bulk messenger RNA stability in Escherichia coli. Besides, rRNA processing, polycistronic RNA selective expression and DNA replication are also governed by RNase E. Previous studies suggest the RNase E cleavage depends on environmental conditions, such as temperature, growth rate, and medium composition. They affect its affinity to specific substrates due to the change of RNA secondary structure or others assistant factors. Therefore, it is important to understand the effect of condition changes and RNase E expression. In this study, we examined the effects of carbon sources, growth rate and starvation on rne gene expression. The results reveal that carbon source and growth rate participate in modulating rne transcripts decay rate. The rne mRNA was more stable in minimal medium with glucose than with acetate, and the decay rate increased with growth rate. All of these suggested RNase E maintained its optimal cellular concentration. Under starvation conditions, we observed that rne transcripts dramatically degraded and rne promoters activity were inhibited. Moreover, nutrient deprivation down- regulated RNase E concentration by global regulator (p)ppGpp. Indirect evidence suggests that the elongation of mRNA halt-life resulted from starvation adjust the cell in response to the environment changes.