We previously reported the isolation of a 21.5-kb genomic DNA fragment from Pseudomonas sp. strain ADP, which contains the atzA gene, encoding the first metabolic step for the degradation of the herbicide atrazine (M. de Souza, L. P. Wackett, K. L. Boundy-Mills, R. T. Mandelbaum, and M. J. Sadowsky, Appl. Environ. Microbiol. 61:3373-3378, 1995). In this study, we show that this fragment also contained the second gene of the atrazine metabolic pathway, atzB. AtzB catalyzed the transformation of hydroxyatrazine to N-isopropylammelide. The product was identified by use of high-performance liquid chromatography, mass spectrometery, and nuclear magnetic resonance spectroscopy. Tn5 mutagenesis of pMD1 was used to determine that atzB was located 8 kb downstream of atzA. Hydroxyatrazine degradation activity was localized to a 4.0-kb ClaI fragment, which was subcloned into the vector pACYC184 to produce plasmid pATZB-2. The DNA sequence of this region was determined and found to contain two large overlapping divergent open reading frames, ORF1 and ORF2. ORF1 was identified as the coding region of atzB by demonstrating that (i) only ORF1 was transcribed in Pseudomonas sp. strain ADP, (ii) a Tn5 insertion in ORF2 did not disrupt function, and (iii) codon usage was consistent with ORF1 being translated. AtzB had 25% amino acid identity with TrzA, a protein that catalyzes a hydrolytic deamination of the s-triazine substrate melamine. The atzA and atzB genes catalyze the first two steps of the metabolic pathway in a bacterium that rapidly metabolizes atrazine to carbon dioxide, ammonia, and chloride.
我们之前报道了从Pseudomonas sp. strain
ADP中分离出的一个21.5 kb的
基因组DNA片段,其中包含atzA
基因,该
基因编码
除草剂atrazine降解的第一步代谢。在这项研究中,我们展示了该片段还包含atzB的第二个
基因。AtzB催化羟基atrazine转化为N-异丙基ammelide。产物通过高效
液相色谱、质谱和核磁共振光谱鉴定。使用Tn5突变pMD1以确定atzB位于atzA的下游8 kb。羟基atrazine降解活性定位于4.0 kb的ClaI片段中,该片段被亚克隆到pACYC184载体中产生质粒pATZB-2。该区域的DNA序列被确定,并发现其中包含两个大的重叠的相反的开放阅读框,ORF1和ORF2。通过证明(i)只有ORF1在Pseudomonas sp. strain
ADP中转录,(ii) ORF2中的Tn5插入没有破坏功能,(iii)密码子使用与ORF1的翻译一致,确定ORF1是atzB的编码区域。AtzB与TrzA具有25%的
氨基酸同源性,TrzA是一种催化s-三嗪底物
蜜胺的
水解脱胺的蛋白质。atzA和atzB
基因在一种快速代谢atrazine为
二氧化碳、
氨和
氯化物的细菌中催化代谢途径的前两步。