ISSN:
1365-2958
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
,
Medicine
Notes:
Further genetic evidence is provided here that Bradyrhizobium japonieum possesses a mitochondria-like electron-transport pathway: 2[H]→UQ→bc1→c→aa3→O2. Two Tn5-induced mutants, COX122 and COX132, having cytochrome c oxidase-negative phenotypes, were obtained and characterized. Mutant COX122 was defective in a novel gene, named cycM, which was responsible for the synthesis of a c-type cytochrome with an Mr, of 20000 (20K). This 20K cytochrome c appeared to catalyse electron transport from the cytochrome bc1, complex to the aa3-type terminal oxidase and, unlike mitochondrial cytochrome c, was membrane-bound in B. japonicum. The Tn5 insertion of mutant COX132 was localized in coxA, the structural gene for subunit I of cytochrome aa3. This finding also led to the cloning and sequencing of the corresponding wild-type coxA gene that encoded a 541 -amino-acid protein with a predicted Mr of 59247. The CoxA protein shared about 60% sequence identity with the cytochrome aa3 subunit I of mitochondria. The B. japonicum cycM and coxA mutants were able to fix nitrogen in symbiosis with soybean (Fix+). In contrast, mutants described previously which lacked the bc1 complex did not develop into endosymbiotic bacteroids and were thus Fix−. The data suggest that a symbiosis-specific respiratory chain exists in B. japonicum in which the electrons branch off at the bc1 complex.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-2958.1990.tb00576.x
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