Nakamura C, Burgess J G, Sode K, Matsunaga T
Department of Biotechnology, Tokyo University of Agriculture and Technology, Japan.
J Biol Chem. 1995 Nov 24;270(47):28392-6. doi: 10.1074/jbc.270.47.28392.
Magnetospirillum sp. AMB-1 is a freshwater magnetic bacterium which synthesizes intracellular particles of magnetite (Fe3O4). A genomic DNA fragment required for synthesis of magnetic particles was previously isolated from a nonmagnetic transposon Tn5 mutant. We have determined the complete nucleotide sequence of this fragment. The 2975-base pair region contains two putative open reading frames. One open reading frame, designated magA, encodes a polypeptide which is homologous to the cation efflux proteins, the Escherichia coli potassium ion-translocating protein, KefC, and the putative Na+/H(+)-antiporter, NapA, from Enterococcus hirae. Northern hybridization demonstrated that the magA mRNA transcript is 1.3 kilobases in size, corresponding to the size of the magA gene. A functional promoter was located upstream from the magA gene, and the transcription in AMB-1 was regulated by environmental iron concentration. Vesicles isolated from E. coli in which the MagA protein was expressed exhibited iron accumulation ability. We consider that the MagA protein is an iron transport involved in the synthesis of magnetic particles in AMB-1.
嗜磁螺菌AMB-1是一种淡水磁性细菌，可合成细胞内的磁铁矿颗粒（Fe3O4）。先前从非磁性转座子Tn5突变体中分离出了合成磁性颗粒所需的基因组DNA片段。我们已经确定了该片段的完整核苷酸序列。这个2975个碱基对的区域包含两个推定的开放阅读框。其中一个开放阅读框，命名为magA，编码一种与阳离子外流蛋白、大肠杆菌钾离子转运蛋白KefC以及来自希氏肠球菌的推定Na+/H(+)反向转运蛋白NapA同源的多肽。Northern杂交表明，magA mRNA转录本大小为1.3千碱基，与magA基因的大小相对应。在magA基因上游定位到了一个功能性启动子，并且AMB-1中的转录受环境铁浓度的调节。从表达MagA蛋白的大肠杆菌中分离出的囊泡表现出铁积累能力。我们认为MagA蛋白是参与AMB-1中磁性颗粒合成的一种铁转运蛋白。
