Ozenberger B A, Nahlik M S, McIntosh M A
J Bacteriol. 1987 Aug;169(8):3638-46. doi: 10.1128/jb.169.8.3638-3646.1987.
Three genes were shown to provide functions specific for ferric enterobactin transport in Escherichia coli: fepA encoded the outer membrane receptor, fepB produced a periplasmic protein, and the fepC product was presumably a component of a cytoplasmic membrane permease system for this siderophore. A 10.6-kilobase-pair E. coli chromosomal EcoRI restriction fragment containing the fepB and fepC genes was isolated from a genomic library constructed in the vector pBR328. Both cistrons were localized on this clone (pITS24) by subcloning and deletion and insertion mutagenesis to positions that were separated by approximately 2.5 kilobases. Within this region, insertion mutations defining an additional ferric enterobactin transport gene (fepD) were isolated, and polarity effects from insertions into fepB suggested that fepD is encoded downstream on the same transcript. A 31,500-dalton FepC protein and a family of FepB polypeptides ranging from 34,000 to 37,000 daltons were identified in E. coli minicells, but the product of fepD was not detectable by this system. Another insertion mutation between entF and fepC was also shown to disrupt iron transport via enterobactin and thus defined the fepE locus; fepE weakly expressed a 43,000-dalton protein in minicells. It is proposed that these newly identified genes, fepD and fepE, provide functions which act in conjunction with the fepC product to form the ferric enterobactin-specific cytoplasmic membrane permease. An additional 44,000-dalton protein was identified and shown to be expressed from a gene that is situated between fepB and entE and that is transcribed in the direction opposite that of fepB. Although the function of this protein is uncharacterized, its membrane location suggests that it too may function in iron transport.
fepA编码外膜受体，fepB产生一种周质蛋白，fepC产物可能是这种铁载体的细胞质膜通透酶系统的一个组分。从构建于载体pBR328中的基因组文库中分离出一个含fepB和fepC基因的10.6千碱基对的大肠杆菌染色体EcoRI限制片段。通过亚克隆以及缺失和插入诱变，这两个顺反子都定位在这个克隆（pITS24）上，它们相隔约2.5千碱基。在这个区域内，分离出了定义另一个铁肠杆菌素转运基因（fepD）的插入突变体，插入fepB产生的极性效应表明fepD在同一转录本的下游编码。在大肠杆菌小细胞中鉴定出了一个31,500道尔顿的FepC蛋白和一系列分子量在34,000到37,000道尔顿之间的FepB多肽，但该系统检测不到fepD的产物。还发现entF和fepC之间的另一个插入突变也会破坏通过肠杆菌素的铁转运，从而确定了fepE位点；fepE在小细胞中弱表达一种43,000道尔顿的蛋白。有人提出，这些新鉴定出的基因fepD和fepE提供与fepC产物协同作用以形成铁肠杆菌素特异性细胞质膜通透酶的功能。还鉴定出了另一种44,000道尔顿的蛋白，它由位于fepB和entE之间且转录方向与fepB相反的一个基因表达。尽管该蛋白的功能尚未明确，但它在膜上的定位表明它也可能在铁转运中发挥作用。
