Parsot C
EMBO J. 1986 Nov;5(11):3013-9. doi: 10.1002/j.1460-2075.1986.tb04600.x.
The Bacillus subtilis genes encoding threonine synthase (thrC) and homoserine kinase (thrB) have been cloned via complementation of Escherichia coli thr mutants. Determination of their nucleotide sequences indicates that the thrC stop codon overlaps the thrB start codon; this genetic organization suggests that the two genes belong to the same operon, as in E. coli. However, the gene order is thrC-thrB in B. subtilis whereas it is thrB-thrC in the thr operon of E. coli. This inversion of the thrC and thrB genes between E. coli and B. subtilis is indicative of a possible independent construction of the thr operon in these two organisms. In other respects, comparison of the predicted amino acid sequences of the B. subtilis and E. coli threonine synthases with that of Saccharomyces cerevisiae threonine dehydratase and that of E. coli D-serine dehydratase revealed extensive homologies between these pyridoxal phosphate-dependent enzymes. This sequence homology, which correlates with similarities in the catalytic mechanisms of these enzymes, indicates that these proteins, catalyzing different reactions in different metabolic pathways, may have evolved from a common ancestor.
通过对大肠杆菌苏氨酸突变体的互补作用，已克隆出编码苏氨酸合酶（thrC）和高丝氨酸激酶（thrB）的枯草芽孢杆菌基因。对它们核苷酸序列的测定表明，thrC的终止密码子与thrB的起始密码子重叠；这种基因组织表明这两个基因属于同一个操纵子，就像在大肠杆菌中一样。然而，在枯草芽孢杆菌中基因顺序是thrC - thrB，而在大肠杆菌的thr操纵子中是thrB - thrC。大肠杆菌和枯草芽孢杆菌中thrC和thrB基因的这种倒置表明在这两种生物体中thr操纵子可能是独立构建的。在其他方面，将枯草芽孢杆菌和大肠杆菌苏氨酸合酶的预测氨基酸序列与酿酒酵母苏氨酸脱水酶和大肠杆菌D - 丝氨酸脱水酶的序列进行比较，发现这些依赖磷酸吡哆醛的酶之间存在广泛的同源性。这种序列同源性与这些酶催化机制的相似性相关，表明这些在不同代谢途径中催化不同反应的蛋白质可能起源于一个共同的祖先。
