Algae, Tree, Herbs, Bush, Shrub, Grasses, Vines, Fern, Moss, Spermatophyta, Bryophyta, Fern Ally, Flower, Photosynthesis, Eukaryote, Prokaryote, carbohydrate, vitamins, amino acids, botany, lipids, proteins, cell, cell wall, biotechnology, metabolities, enzymes, agriculture, horticulture, agronomy, bryology, plaleobotany, phytochemistry, enthnobotany, anatomy, ecology, plant breeding, ecology, genetics, chlorophyll, chloroplast, gymnosperms, sporophytes, spores, seed, pollination, pollen, agriculture, horticulture, taxanomy, fungi, molecular biology, biochemistry, bioinfomatics, microbiology, fertilizers, insecticides, pesticides, herbicides, plant growth regulators, medicinal plants, herbal medicines, chemistry, cytogenetics, bryology, ethnobotany, plant pathology, methodolgy, research institutes, scientific journals, companies, farmer, scientists, plant nutrition
Select Language:
 
   
 
 
Can't find? Try Deep Search with ePlantScience.com  
 
Share |
 
   
Main Menu
If navigation gets difficult, please click the main subject or sitemap to get the list of sub-categories
 
 
 
 
 
Related websites
 
 
 
 
 
 
 
 
Section: Genetics » Regulation of Gene Expression » Operon Circuits in Prokaryotes
 
 
If you like this page, please click:  
 
 
  Signal transduction and ‘two component regulatory system’
 
     
 
Content
⇒ Regulation of Gene Expression 1.  Operon Circuits in Bacteria and other Prokaryotes
⇒ Induction and repression
⇒ Inducer and co-repressor
⇒ The operon model for transcriptional regulation 
⇒ The tryptophan operon in bacteria (E. coli and Salmonella)
⇒ Tryptophan (trp) repressor controls three sets of genes
⇒ Negative and Positive Controls of Transcription
⇒ Substitution of Sigma Factor and Control of Transcription
⇒ Multiple sigma factors in E. coli 
⇒ Sporulation in bacteria
⇒ DNA sequences controlling transcription 
⇒ DNA sequences for CAP, RNA polymerase and lac-repressor
⇒ Identification of starting point
⇒ Pribnow box and other sequences common to DNA regions upstream to several operons
⇒ Regulation by DNA rearrangements
⇒ Post-transcriptional regulation
⇒ Leader sequences and attenuators
⇒ Autogenous regulation of translation
⇒ Regulation by alternative splicing
⇒ Regulation by-anti-sense RNA
⇒ Repression and activation of translation
⇒ Feedback inhibition
⇒ Signal transduction and ‘two component regulatory system’
Signal Transduction and 'Two Component Regulatory Systems'
In prokaryotes, a wide variety of stimuli are sensed and transduced leading to altered gene expression. Important examples in E. coli, include chemotaxis, nitrogen assimilation and outer membrane protein expression. Two sets of proteins, bearing sequence similarities, are known to be involved in these regulatory systems, which are, therefore, described as 'two component regulatory systems'. The first component is a protein kinase, described as 'kinase', that autophosphorylates (using ATP) a histidine residue, and transfers its phosphoryl group to an aspartate residue of the second component described as 'regulator'. Finally, a phosphatase activity may reset the system by restoring the regulator to its unphosphorylated state. Regulator phosphate levels are controlled in response to environmental condition.

The above signal transduction, using 'two component systems' can be illustrated using the following three example.

Bacterial chemotaxis
In homogenous environment, E. coli swims smoothly, but it moves towards or away from wide variety of compounds classified as 'attractants' or 'repellents' respectively. This mechanism involves a post-translational regulation of gene expression, involving reversible phosphorylation of two proteins, CheA (kinase) and CheY (regulator).

Nitrogen assimilation
Many species of bacteria regulate both the amount and the activity of 'glutamine synthetase' enzyme in response to nitrogen availability. The gene for this enzyme is glnA and its major promoter is glnAp2. Transcription of the gene is regulated by a two component system (NtrB = kinase, NtrC = regulator). NtrB autophosphorylates and transfers its phosphate group to NtrC, which in its phosphorylated form activates glnAp2.The phosphorylation of NtrC is regulated by nitrogen availability through another protein called 'PII'.

Outer membrane protein expression
Earlier in this section, we discussed regulation of expression of genes ompC and ompF (meant for outer membrane proteins) at the translational level using antisense RNA. Another mechanism at the transcriptional level involves a two component system (EnvZ = kinase; OmpR = regulator). EnvZ autophosphorylates and transfers its phosphate group to OmpR, which in its phosphorylated form, stimulates expression of ompF under 'low osmolarity' conditions and that of ompC under 'high osmolarity' condition. Phosphorylation of OmpR is also regulated due to hydrolysis in the joint presence of EnvZ and ATP.

For details of the above regulatory mechariisms and signal transduction, the readers are advised to consult Ann. Rev. Biochem. 60 : 401-441 (1991).
 
     






     
     
 
 
     
 
Copyrights 2009 © ePlantScience.com