Gavini N, Davidson B E
Russell Grimwade School of Biochemistry, University of Melbourne, Parkville, Victoria, Australia.
J Biol Chem. 1991 Apr 25;266(12):7750-3.
In Escherichia coli, the expression of the phenylalanine biosynthetic enzyme chorismate mutase/prephenate dehydratase, encoded by pheA, is elevated in strains carrying pheR mutants. By constructing a series of pheA''cat'lacZ fusions with different endpoints for deletions of the pheA regulatory DNA, the site of action of the pheR product on pheA expression was determined to be the pheA attenuator. Southern blot analysis of chromosomal DNA from a pheR374 strain showed it to carry a deletion of pheR and the flanking DNA on each side. This deletion resulted in a decrease of approximately 30% in the intracellular concentration of tRNA(Phe), the pheR product. The expression of the pheST operon, which encodes the two subunits of phenylalanyl-tRNA synthetase and which is also regulated by attenuation control involving phenylalanyl-tRNA(Phe), was increased 5-fold by the pheR374 allele. No effect of pheR on pheST expression was seen in a pheST(att-) strain. It was concluded that the elevated expression of pheA and pheST in pheR mutants is a consequence of a lower frequency of transcription termination in the attenuator caused by lower levels of phenylalanyl-tRNA(Phe).
在大肠杆菌中，由pheA编码的苯丙氨酸生物合成酶分支酸变位酶/预苯酸脱水酶的表达，在携带pheR突变体的菌株中会升高。通过构建一系列具有不同pheA调控DNA缺失端点的pheA''cat'lacZ融合体，确定pheR产物对pheA表达的作用位点是pheA衰减子。对pheR374菌株的染色体DNA进行Southern印迹分析表明，它携带pheR及其两侧侧翼DNA的缺失。这种缺失导致pheR产物即tRNA（Phe）的细胞内浓度下降约30%。编码苯丙氨酰-tRNA合成酶两个亚基且同样受涉及苯丙氨酰-tRNA（Phe）的衰减控制调节的pheST操纵子的表达，被pheR374等位基因提高了5倍。在pheST（att-）菌株中未观察到pheR对pheST表达有影响。得出的结论是，pheR突变体中pheA和pheST表达升高是由于苯丙氨酰-tRNA（Phe）水平较低导致衰减子转录终止频率降低的结果。
