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首页> 外文期刊>Journal of bacteriology >Evidence that a novel tetracycline resistance gene found on two Bacteroides transposons encodes an NADP-requiring oxidoreductase.
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Evidence that a novel tetracycline resistance gene found on two Bacteroides transposons encodes an NADP-requiring oxidoreductase.

机译：在两个拟杆菌的转座子上发现一个新的四环素抗性基因的证据编码了需要NADP的氧化还原酶。

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Two transposons, Tn4351 and Tn4400, which were originally isolated from the obligate anaerobe Bacteroides fragilis, carry a tetracycline resistance (Tcr) gene that confers resistance only on aerobically grown Escherichia coli. This aerobic Tcr gene, designated tetX, has been shown previously to act by chemically modifying tetracycline in a reaction that appears to require oxygen. We have now obtained the DNA sequence of tetX and 0.6 kb of its upstream region from Tn4400. Analysis of the DNA sequence of tetX revealed that this gene encoded a 43.7-kDa protein. The deduced amino acid sequence of the amino terminus of the protein had homology with a number of enzymes, all of which had in common a requirement for NAD(P). In an earlier study, we had observed that disrupted cells, unlike intact cells, could not carry out the alteration of tetracycline. We have now shown that if NADPH (1 mM) is added to the disrupted cell preparation, alteration of tetracycline occurs. Thus, TetX appears to be an NADP-requiring oxidoreductase. Tn4400 conferred a fivefold-lower level of tetracycline resistance than Tn4351. This finding appears to be due to a lower level of expression of the tetX on Tn4400, because the activity of a tetX-lacZ fusion from Tn4400 was 10-fold lower than that of the same fusion from Tn4351. A comparison of the sequence of the tetX region on Tn4351 with that on Tn4400 showed that the only difference between the upstream regions of the two transposons was a 4-base change 350 bp upstream of the start of the tetX coding region. The 4-base change difference creates a good consensus -35 region on Tn4351 that is not present on Tn4400 and could be creating an extra promoter.
机译：两个转座子，Tn4351和Tn4400，最初从专性的厌氧拟杆菌分离，带有四环素抗性（Tcr）基因，仅在需氧生长的大肠杆菌上赋予抗性。该好氧Tcr基因（称为tetX）先前已显示出在化学反应中似乎需要氧气的情况下通过化学修饰四环素发挥作用。现在，我们已经从Tn4400获得了tetX的DNA序列及其0.6 kb的上游区域。对tetX的DNA序列进行分析后发现，该基因编码一个43.7 kDa的蛋白质。推导的蛋白质氨基末端的氨基酸序列与多种酶具有同源性，所有这些酶均共同需要NAD（P）。在较早的研究中，我们观察到破坏的细胞与完整的细胞不同，不能进行四环素的改变。现在我们已经表明，如果将NADPH（1 mM）添加到破裂的细胞制备物中，则会发生四环素改变。因此，TetX似乎是需要NADP的氧化还原酶。 Tn4400的四环素抗性比Tn4351低五倍。这一发现似乎是由于tetX在Tn4400上的表达水平较低，因为来自Tn4400的tetX-lacZ融合体的活性比来自Tn4351的相同融合体的活性低10倍。 Tn4351上的tetX区序列与Tn4400上的tetX区序列的比较表明，两个转座子的上游区域之间唯一的区别是tetX编码区起始上游350 bp的4个碱基的变化。 4个碱基的变化差异在Tn4351上创建了一个良好的共有-35区域，该区域在Tn4400上不存在，可能会创建一个额外的启动子。

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