Van Soom C, Verreth C, Sampaio M J, Vanderleyden J
F.A. Janssens Laboratory of Genetics, Catholic University of Leuven, Heverlee, Belgium.
Mol Gen Genet. 1993 May;239(1-2):235-40. doi: 10.1007/BF00281623.
In Bradyrhizobium japonicum, Tn5 insertions in a particular chromosomal DNA fragment result in a Hup- phenotype in free-living conditions without affecting hydrogenase (Hup) activity in the symbiotic state. By determination of the nucleotide sequence of this region, we were able to identify the nature of the inactivated genes. The fragment is located 9 kb downstream of the hydrogenase structural genes and contains one incomplete and three complete open reading frames. They are designated hypD', hypE, hoxX and hoxA respectively, since the deduced amino acid sequences display very strong homology with genes involved in the regulation of hydrogenase activity in Escherichia coli, Rhodobacter capsulatus, Azotobacter vinelandii (hypD' and hypE) and Alcaligenes eutrophus (hoxX and hoxA). This is the first report on transcriptional activators of the hup genes in B. japonicum. Implications of these findings with respect to regulation of hydrogenase synthesis by hydrogen, oxygen and nickel in free-living B. japonicum are discussed.
在日本慢生根瘤菌中，特定染色体DNA片段中的Tn5插入在自由生活条件下导致吸氢（Hup）阴性表型，而不影响共生状态下的氢化酶（Hup）活性。通过测定该区域的核苷酸序列，我们能够鉴定失活基因的性质。该片段位于氢化酶结构基因下游9 kb处，包含一个不完整和三个完整的开放阅读框。它们分别被命名为hypD'、hypE、hoxX和hoxA，因为推导的氨基酸序列与大肠杆菌、荚膜红细菌、维涅兰德固氮菌（hypD'和hypE）以及真养产碱菌（hoxX和hoxA）中参与氢化酶活性调节的基因具有很强的同源性。这是关于日本慢生根瘤菌中hup基因转录激活因子的首次报道。讨论了这些发现对自由生活的日本慢生根瘤菌中氢气、氧气和镍对氢化酶合成调节的意义。
