ABSTRACT
Ralstonia
sp. strain U2 metabolizes naphthalene via gentisate to central metabolites. We have cloned and sequenced a 21.6-kb region spanning the
nag
genes. Upstream of the pathway genes are
nagY,
homologous to chemotaxis proteins, and
nagR,
a regulatory gene of the LysR family. Divergently transcribed from
nagR
are the genes for conversion of naphthalene to gentisate (
nagAaGHAbAcAdBFCQED
) (S. L. Fuenmayor, M. Wild, A. L. Boyes, and P. A. Williams, J. Bacteriol. 180:2522–2530, 1998), which except for the insertion of
nagGH
, encoding the salicylate 5-hydroxylase, are homologous to and in the same order as the genes in the classical upper pathway operon described for conversion of naphthalene to salicylate found in the NAH7 plasmid of
Pseudomonas putida
PpG7. Downstream of
nahD
is a cluster of genes (
nagJIKLMN
) which are probably cotranscribed with
nagAaGHAbAcAdBFCQED
as a single large operon. By cloning into expression vectors and by biochemical assays, three of these genes (
nagIKL
) have been shown to encode the enzymes involved in the further catabolism of gentisate to fumarate and pyruvate. NagI is a gentisate 1,2-dioxygenase which converts gentisate to maleylpyruvate and is also able to catalyze the oxidation of some substituted gentisates. NagL is a reduced glutathione-dependent maleylpyruvate isomerase catalyzing the isomerization of maleylpyruvate to fumarylpyruvate. NagK is a fumarylpyruvate hydrolase which hydrolyzes fumarylpyruvate to fumarate and pyruvate. The three other genes (
nagJMN
) have also been cloned and overexpressed, but no biochemical activities have been attributed to them. NagJ is homologous to a glutathione
S
-transferase, and NagM and NagN are proteins homologous to each other and to other proteins of unknown function. Downstream of the operon is a partial sequence with homology to a transposase.
摘要
Ralstonia
菌株 U2 通过庆大霉素将萘代谢为中心代谢产物。我们克隆并测序了一个 21.6 kb 的区域,该区域跨越了
nag
基因的 21.6-kb 区域。途径基因的上游是
nagY、
与趋化蛋白同源,以及
nagR、
是 LysR 家族的一个调控基因。与
nagR
与 nagR 分歧转录的基因是将萘转化为庆大霉素的基因 (
nagAaGHAbAcAdBFCQED
)(S. L. Fuenmayor、M. Wild、A. L. Boyes 和 P. A. Williams,J. Bacteriol.180:2522-2530, 1998),其中除了插入了
nagGH
编码水杨酸 5-羟化酶的基因外,与萘转化为水杨酸的经典上途径操作子中的基因同源,且顺序相同。
假单胞菌
PpG7。在
nahD
的下游是一组基因(
nagJIKLMN
可能与
nagAaGHAbAcAdBFCQED
作为一个单一的大操作子。通过克隆表达载体和生化试验,这些基因中有三个(
nagIKL
) 编码参与将龙葵酯进一步分解为富马酸和丙酮酸的酶。NagI 是一种龙葵酯 1,2-二氧 化酶,能将龙葵酯转化为马来酰丙酮酸,还能催化某些取代的龙葵酯的氧化。NagL 是一种依赖还原型谷胱甘肽的马来酰丙酮酸异构酶,催化马来酰丙酮酸与富马酰丙酮酸的异构化。NagK 是富马酸丙酮酸水解酶,可将富马酸丙酮酸水解为富马酸和丙酮酸。其他三个基因(
nagJMN
)也已被克隆和过表达,但它们没有任何生化活性。NagJ 与谷胱甘肽
S
-转移酶同源,NagM 和 NagN 与其他功能不明的蛋白质同源。操作子的下游是与转座酶同源的部分序列。