Creeger E S, Schulte T, Rothfield L I
J Biol Chem. 1984 Mar 10;259(5):3064-9.
The role of sfrB and rfaH genes in the regulation of expression of membrane glycosyltransferases was studied in Escherichia coli and Salmonella typhimurium. The transferase enzymes form part of a multienzyme system involved in biosynthesis of the polysaccharide core of Gram-negative bacterial lipopolysaccharides. Several sfrB mutants of E. coli showed reductions of 90-98% in the activities of two of the glycosyltransferases (UDP-galactose:(glucosyl)lipopolysaccharide 1,6-galactosyltransferase and UDP-glucose: (glucosyl)lipopolysaccharide 1,3-glucosyltransferase). Introduction of a recombinant ColE1 plasmid restored the transferase levels to normal and simultaneously corrected the F-factor defects that also characterize sfrB mutants; recombinant plasmids containing other regions of the E. coli chromosome were ineffective. An amber mutation of the S. typhimurium rfaH gene (thought to be the homologue of the E. coli sfrB gene) resulted in 97% loss of activity of the Salmonella UDP-galactose:(glucosyl)lipopolysaccharide galactosyltransferase. Antibody precipitation studies showed that the loss of enzyme activity in the amber mutant was associated with a corresponding decrease in amount, but not in size, of the transferase protein, indicating that the gene is not the structural gene for the S. typhimurium galactosyltransferase. Taken together, the results indicate that the sfrB(rfaH) gene acts as a positive regulatory element in expression of multiple glycosyltransferases in E. coli and S. typhimurium.
在大肠杆菌和鼠伤寒沙门氏菌中研究了sfrB和rfaH基因在膜糖基转移酶表达调控中的作用。转移酶是革兰氏阴性菌脂多糖多糖核心生物合成相关多酶系统的一部分。大肠杆菌的几个sfrB突变体显示两种糖基转移酶（UDP-半乳糖：(葡糖基)脂多糖1,6-半乳糖基转移酶和UDP-葡萄糖：(葡糖基)脂多糖1,3-葡糖基转移酶）的活性降低了90 - 98%。导入重组ColE1质粒可使转移酶水平恢复正常，并同时纠正了sfrB突变体所具有的F因子缺陷；含有大肠杆菌染色体其他区域的重组质粒则无效。鼠伤寒沙门氏菌rfaH基因（被认为是大肠杆菌sfrB基因的同源物）的琥珀突变导致沙门氏菌UDP-半乳糖：(葡糖基)脂多糖半乳糖基转移酶活性丧失97%。抗体沉淀研究表明，琥珀突变体中酶活性的丧失与转移酶蛋白量的相应减少有关，但与蛋白大小无关，这表明该基因不是鼠伤寒沙门氏菌半乳糖基转移酶的结构基因。综合来看，结果表明sfrB(rfaH)基因在大肠杆菌和鼠伤寒沙门氏菌中多种糖基转移酶的表达中起正调控元件的作用。
