Regulation of the degradative pathway enzymes coded for by the TOL plasmid (pWWO) from Pseudomonas putida mt-2
Regulation of the degradative pathway enzymes coded for by the TOL plasmid (pWWO) from Pseudomonas putida mt-2
复制标题
恶臭假单胞菌 mt-2 的 TOL 质粒 (pWWO) 编码的降解途径酶的调节
作者：
M. Worsey;F. Franklin;P. Williams
恶臭假单胞菌 mt-2 携带一个质粒（TOL，pWWO），该质粒编码一组酶，负责甲苯、间二甲苯和对二甲苯分别通过苯甲酸盐、间和对甲苯甲酸盐分解代谢为中心代谢物，随后通过元裂解途径。该途径结构基因突变菌株的表征表明，负责进一步降解间甲苯甲酸的酶的诱导剂包括间二甲苯、间甲基苯甲醇和间甲苯甲酸，而负责将间二甲苯氧化成间甲苯甲酸的酶的诱导物包括间二甲苯和间甲基苯甲醇，但不包括间甲苯甲酸。描述了一种调节突变体，其中间二甲苯和间甲基苯甲醇不再诱导任何途径酶，但间甲苯甲酸仍然能够诱导负责其自身降解的酶。在该突变体的回复体中有一些菌株，其中所有酶都组成型表达并且不被间二甲苯进一步诱导。提出了一种用于调节途径的模型，其中酶位于两个调节块中，这两个调节块受两个调节基因产物的控制。该模型与之前提出的恶臭假单胞菌 MT20 的 TOL20 质粒上同功能途径的调节模型基本相同。
Pseudomonas putida mt-2 carries a plasmid (TOL, pWWO) which codes for a single set of enzymes responsible for the catabolism of toluene and m- and p-xylene to central metabolites by way of benzoate and m- and p-toluate, respectively, and subsequently by a meta cleavage pathway. Characterization of strains with mutations in structural genes of this pathway demonstrates that the inducers of the enzymes responsible for further degradation of m-toluate include m-xylene, m-methylbenzyl alcohol, and m-toluate, whereas the inducers of the enzymes responsible for oxidation of m-xylene to m-toluate include m-xylene and m-methylbenzyl alcohol but not m-toluate. A regulatory mutant is described in which m-xylene and m-methylbenzyl alcohol no longer induce any of the pathway enzymes, but m-toluate is still able to induce the enzymes responsible for its own degradation. Among revertants of this mutant are some strains in which all the enzymes are expressed constitutively and are not further induced by m-xylene. A model is proposed for the regulation of the pathway in which the enzymes are in two regulatory blocks, which are under the control of two regulator gene products. The model is essentially the same as proposed earlier for the regulation of the isofunctional pathway on the TOL20 plasmid from P. putida MT20.