A rationale for autoinduction of a transcriptional activator: ethanolamine ammonia-lyase (EutBC) and the operon activator (EutR) compete for adenosyl-cobalamin in Salmonella typhimurium.
نویسندگان
چکیده
The ethanolamine utilization (eut) operon of Salmonella typhimurium is controlled by a positive regulatory protein (EutR) which stimulates eut operon expression in response to the simultaneous presence of two effectors, ethanolamine and adenosyl-cobalamin (Ado-B12). Ado-B12 is a cofactor for ethanolamine ammonia-lyase (lyase), the first enzyme in the ethanolamine-degradative pathway. The dependence of this pathway on the use of Ado-B12 as an effector in eut operon induction may be explained by its role in the degradation of ethanolamine and the fact that this cofactor is not always made by S. typhimurium. The eutR gene lies within the eut operon, and its autoinduction is required for maximum operon expression. Evidence is presented that the placement of the eutR regulatory gene within the operon provides a means of balancing the competition between lyase and the regulatory protein for a very small pool of Ado-B12. Since both lyase and the regulatory protein are induced, they can compete more equally for a small pool of Ado-B12. This permits both continued eut operon induction and lyase activity. Two general observations support this model. First, mutations that inactivate lyase allow the operon to be fully induced by a lower level of exogenous cobalamin (CN-B12) than required by a wild-type operon. This increase in sensitivity is measured as a reduction in the apparent Km for operon induction by exogenous CN-B12. Second, the maximum level of operon induction by excess CN-B12 is dictated by the level of EutR regulatory protein, regardless of the level of lyase.
منابع مشابه
Autogenous regulation of ethanolamine utilization by a transcriptional activator of the eut operon in Salmonella typhimurium.
The genes required for use of ethanolamine as a carbon and nitrogen source are encoded by a single operon (eut) whose expression is induced by the simultaneous presence of both ethanolamine and cobalamin (vitamin B12). The action of B12 as an inducer of this operon reflects the fact that this cofactor is required by the degradative enzyme ethanolamine lyase (eutBC). The eutR gene encodes a prot...
متن کاملComparative genomics of ethanolamine utilization.
Ethanolamine can be used as a source of carbon and nitrogen by phylogenetically diverse bacteria. Ethanolamine-ammonia lyase, the enzyme that breaks ethanolamine into acetaldehyde and ammonia, is encoded by the gene tandem eutBC. Despite extensive studies of ethanolamine utilization in Salmonella enterica serovar Typhimurium, much remains to be learned about EutBC structure and catalytic mechan...
متن کاملFunctions required for vitamin B12-dependent ethanolamine utilization in Salmonella typhimurium.
When B12 is available, Salmonella typhimurium can degrade ethanolamine to provide a source of carbon and nitrogen. B12 is essential since it is a cofactor for ethanolamine ammonia-lyase, the first enzyme in ethanolamine breakdown. S. typhimurium makes B12 only under anaerobic conditions; in the presence of oxygen, exogenous B12 must be provided to permit ethanolamine utilization. Genes required...
متن کاملEvidence that a B12-adenosyl transferase is encoded within the ethanolamine operon of Salmonella enterica.
Adenosylcobalamin (Ado-B12) is both the cofactor and inducer of ethanolamine ammonia lyase (EA-lyase), a catabolic enzyme for ethanolamine. De novo synthesis of Ado-B12 by Salmonella enterica occurs only under anaerobic conditions. Therefore, aerobic growth on ethanolamine requires import of Ado-B12 or a precursor (CN-B12 or OH-B12) that can be adenosylated internally. Several known enzymes ade...
متن کاملEthanolamine utilization in Salmonella typhimurium.
Ethanolamine can serve as the sole source of carbon and nitrogen for Salmonella typhimurium if vitamin B12 is present to serve as a cofactor. The pathway for ethanolamine utilization has been investigated in order to understand its regulation and determine whether the pathway is important to the selective forces that have maintained the ability to synthesize B12 in S. typhimurium. We isolated m...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
- Journal of bacteriology
دوره 176 5 شماره
صفحات -
تاریخ انتشار 1994