Xanthine metabolism in Bacillus subtilis: Characterization of the xpt-pbuX operon and evidence for purine- and nitrogen-controlled expression of genes involved in xanthine salvage and catabolism
Xanthine metabolism in Bacillus subtilis: Characterization of the xpt-pbuX operon and evidence for purine- and nitrogen-controlled expression of genes involved in xanthine salvage and catabolism
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DOI：
10.1128/jb.179.8.2540-2550.1997
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发表时间：
1997-04-01
影响因子：
3.2
通讯作者：
Saxild, HH
中科院分区：
文献类型：
--
作者：
Christiansen, LC;Schou, S;Saxild, HH
枯草芽孢杆菌的xpt和pbuX基因被克隆，并且它们的核苷酸序列被确定。xpt基因编码一种特异性的黄嘌呤磷酸核糖转移酶，pbuX基因编码一种黄嘌呤特异性的嘌呤通透酶。这些基因具有重叠的编码区域，并且Northern（RNA）印迹分析表明存在一个操纵子结构。第二个基因pbuX的翻译强烈依赖于第一个基因xpt的翻译。该操纵子的表达受到嘌呤的抑制，效应分子似乎是次黄嘌呤和鸟嘌呤。当次黄嘌呤和鸟嘌呤一起添加时，观察到160倍的抑制。表达的调控在转录水平，并且我们提出存在一种类似于嘌呤生物合成操纵子调控所提出的转录终止 - 抗终止控制机制。当次黄嘌呤作为唯一氮源时，xpt - pbuX操纵子的表达降低。在这些条件下，次黄嘌呤和黄嘌呤降解酶——黄嘌呤脱氢酶的水平被诱导超过80倍。在glnA（谷氨酰胺合成酶）遗传背景下，黄嘌呤脱氢酶水平完全去抑制。尽管发现xpt - pbuX操纵子表达的调控受氮源影响，但在glnA突变株中是正常的。这个结果表明对于xpt - pbuX操纵子转录的抑制和黄嘌呤脱氢酶的诱导存在不同的信号通路。
The xpt and pbuX genes from Bacillus subtilis were cloned, and their nucleotide sequences were determined, The xpt gene encodes a specific xanthine phosphoribosyltransferase, and the pbuX gene encodes a xanthine-specific purine permease, The genes have overlapping coding regions, and Northern (RNA) blot analysis indicated an operon organization, The translation of the second gene, pbuX, was strongly dependent on the translation of the first gene, xpt, Expression of the operon was repressed by purines, and the effector molecules appear to be hypoxanthine and guanine, When hypoxanthine and guanine were added together, a 160-fold repression was observed, The regulation of expression was at the level of transcription, and we propose that a transcription termination-antitermination control mechanism similar to the one suggested for the regulation of the purine biosynthesis operon exists, The expression of the xpt-pbuX operon was reduced when hypoxanthine served as the sole nitrogen source, Under these conditions, the level of the hypoxanthine- and xanthine-degrading enzyme, xanthine dehydrogenase, was induced more than 80-fold, The xanthine dehydrogenase level was completely derepressed in a glnA (glutamine synthetase) genetic background, Although the regulation of the expression of the xpt-pbuX operon was found to be affected by the nitrogen source, it was normal in a glnA mutant strain, This result suggests the existence of different signalling pathways for repression of the transcription of the xpt-pbuX operon and the induction of xanthine dehydrogenase.