Brown K D, Somerville R L
J Bacteriol. 1971 Oct;108(1):386-99. doi: 10.1128/jb.108.1.386-399.1971.
Mutants of Escherichia coli K-12 were isolated in which the synthesis of the following, normally repressible enzymes of aromatic biosynthesis was constitutive: 3-deoxy-d-arabinoheptulosonic acid 7-phosphate (DAHP) synthetases (phe and tyr), chorismate mutase T-prephenate dehydrogenase, and transaminase A. In the wild type, DAHP synthetase (phe) was multivalently repressed by phenylalanine plus tryptophan, whereas DAHP synthetase (tyr), chorismate mutase T-prephenate dehydrogenase, and transaminase A were repressed by tyrosine. DAHP synthetase (tyr) and chorismate mutase T-prephenate dehydrogenase were also repressed by phenylalanine in high concentration (10(-3)m). Besides the constitutive synthesis of DAHP synthetase (phe), the mutants had the same phenotype as strains mutated in the tyrosine regulatory gene tyrR. The mutations causing this phenotype were cotransducible with trpA, trpE, cysB, and pyrF and mapped in the same region as tyrR at approximately 26 min on the chromosome. It is concluded that these mutations may be alleles of the tyrR gene and that synthesis of the enzymes listed above is controlled by this gene. Chorismate mutase P and prephenate dehydratase activities which are carried on a single protein were repressed by phenylalanine alone and were not controlled by tyrR. Formation of this protein is presumed to be controlled by a separate, unknown regulator gene. The heat-stable phenylalanine transaminase and two enzymes of the common aromatic pathway, 5-dehydroquinate synthetase and 5-dehydroquinase, were not repressible under the conditions studied and were not affected by tyrR. DAHP synthetase (trp) and tryptophan synthetase were repressed by tryptophan and have previously been shown to be under the control of the trpR regulatory gene. These enzymes also were unaffected by tyrR.
分离出了大肠杆菌K - 12的突变体，其中以下通常可被阻遏的芳香族生物合成酶的合成是组成型的：3 - 脱氧 - D - 阿拉伯庚酮糖酸7 - 磷酸（DAHP）合成酶（苯丙氨酸和酪氨酸型）、分支酸变位酶T - 预苯酸脱氢酶和转氨酶A。在野生型中，DAHP合成酶（苯丙氨酸型）受苯丙氨酸加色氨酸多价阻遏，而DAHP合成酶（酪氨酸型）、分支酸变位酶T - 预苯酸脱氢酶和转氨酶A受酪氨酸阻遏。高浓度（10⁻³m）的苯丙氨酸也能阻遏DAHP合成酶（酪氨酸型）和分支酸变位酶T - 预苯酸脱氢酶。除了DAHP合成酶（苯丙氨酸型）的组成型合成外，这些突变体与酪氨酸调节基因tyrR发生突变的菌株具有相同的表型。导致这种表型的突变与trpA、trpE、cysB和pyrF共转导，并定位在染色体上与tyrR相同的区域，约在26分钟处。得出的结论是，这些突变可能是tyrR基因的等位基因，上述酶的合成受该基因控制。由单一蛋白质承担的分支酸变位酶P和预苯酸脱水酶活性仅受苯丙氨酸阻遏，不受tyrR控制。推测该蛋白质的形成受一个单独的、未知的调节基因控制。热稳定的苯丙氨酸转氨酶以及共同芳香族途径的两种酶，5 - 脱氢奎尼酸合成酶和5 - 脱氢奎尼酸酶，在所研究的条件下不可被阻遏，也不受tyrR影响。DAHP合成酶（色氨酸型）和色氨酸合成酶受色氨酸阻遏，先前已证明受trpR调节基因控制。这些酶也不受tyrR影响。
