Quay S C, Kline E L, Oxender D L
Proc Natl Acad Sci U S A. 1975 Oct;72(10):3921-4. doi: 10.1073/pnas.72.10.3921.
The regulation of the transport of leucine, isoleucine, and valine in Escherichia coli B/r was studied in a mutant with a complete deletion of the leucine biosynthetic operon and a temperature-sensitive leucyl-tRNA synthetase [L-leucine:tRNALeu ligase (AMP-forming), EC 6.1.1.4]. Under conditions of excess leucine and a functional leucyl-tRNA synthetase transport activity was repressed. Shifting the culture to a temperature at which the activation of leucine to an appropriate tRNA species became growth-rate-limiting led to a large increase in the high-affinity transport of leucine, isoleucine, and valine (system LIV-I) while the uptake of histidine and proline was unchanged. A similar increase was observed for branched-chain amino-acid binding protein activity. The temperature change did not alter the transport activity for any of these substrates or the level of the binding proteins in an isogenic strain with a normal leucyl-tRNA synthetase. The increase in transport activity observed in the mutant was prevented by inhibitors of protein and RNA synthesis and probably represents an increase in the differential rate of synthesis of the protein(s) required for transport. These experiments demonstrate that the repression of branched-chain amino-acid transport involves the interaction of leucine with its aminoacyl-tRNA synthetase and its cognate leucyl-tRNA species.
在一株完全缺失亮氨酸生物合成操纵子且带有温度敏感型亮氨酰 - tRNA合成酶[L - 亮氨酸:tRNALeu连接酶(AMP形成), EC 6.1.1.4]的大肠杆菌B/r突变体中,研究了亮氨酸、异亮氨酸和缬氨酸的转运调控。在亮氨酸过量且亮氨酰 - tRNA合成酶功能正常的条件下,转运活性受到抑制。将培养物转移至一个温度,此时亮氨酸与合适的tRNA种类的活化成为生长速率限制因素,导致亮氨酸、异亮氨酸和缬氨酸的高亲和力转运(系统LIV - I)大幅增加,而组氨酸和脯氨酸的摄取未发生变化。对于支链氨基酸结合蛋白活性也观察到类似的增加。温度变化并未改变同基因菌株(具有正常亮氨酰 - tRNA合成酶)中任何这些底物的转运活性或结合蛋白的水平。在突变体中观察到的转运活性增加被蛋白质和RNA合成抑制剂所阻止,这可能代表转运所需蛋白质的差异合成速率增加。这些实验表明,支链氨基酸转运的抑制涉及亮氨酸与其氨酰 - tRNA合成酶及其同源亮氨酰 - tRNA种类的相互作用。