Iuchi S, Kuritzkes D R, Lin E C
J Bacteriol. 1985 Mar;161(3):1023-8. doi: 10.1128/jb.161.3.1023-1028.1985.
In wild-type Escherichia coli, fumarate reductase encoded by the frd operon is inducible by its substrate in the absence of molecular oxygen and nitrate. Synthesis of this enzyme under permissive conditions requires the fnr+ gene product, which is believed to be a pleiotropic regulatory protein that activates transcription. A spontaneous mutant was isolated in which the expression of the frd operon no longer depended on the presence of fumarate or the fnr+ gene product. Aerobic repression of the operon was abolished, but nitrate repression remained intact. Transductional analysis showed that the mutation was closely linked to the frd locus. The mutant phenotype strongly suggests that repression by molecular oxygen and nitrate is mediated by different mechanisms.
在野生型大肠杆菌中，由frd操纵子编码的延胡索酸还原酶在无氧和无硝酸盐的情况下可被其底物诱导。在允许条件下该酶的合成需要fnr⁺基因产物，据信该产物是一种多效调节蛋白，可激活转录。分离出一个自发突变体，其中frd操纵子的表达不再依赖于延胡索酸或fnr⁺基因产物的存在。该操纵子的需氧抑制被消除，但硝酸盐抑制仍然存在。转导分析表明该突变与frd位点紧密连锁。突变体表型强烈表明分子氧和硝酸盐的抑制是由不同机制介导的。
