Operon control

It transpires that the heat shock genes of one single bacterial species are regulated by different mechanisms. Genes and operons controlled by one particular regulator are called regulons and, if there are at least two regulons in one species induced by the same stress factor, they form a stimulon. 

HTHARAC helix turn helix, arabinose operon control protein E(M)B 0(0) 0(0) 1BL0... 

One mechanism of transcriptional control in prokaryotes, especially of several operons controlling the biosynthesis of amino acids, is attenuation. 

Active repressor from copy 2 can bind to operators normally Both operons controlled normally... 

The trp operon controls the production of tryptophan biosynthetic enzymes at two levels, depending on the intracellular concentrations of tryptophan. When tryptophan levels are high, Trp repressor-tryptophan complexes are formed and Trp repressor binding to the trp operon inhibits transcription. A second level of control is called attenuation and it involves the premature termination of transcription when TRP-tRNATrp is abundant and a termination structure is formed, resulting in the disengagement of RNA polymerase from the DNA. 

Gronewold, T.M.A. and Kaiser, D. (2001). Thenct operon controls the level and lime of C-signal production for M. xanthus development. Mol. Microbiol. 40, 744—756. Gronewold, T.M.A. and Kaiser, D. (2002). act operon control of developmental gene expression in Myxococcus xanthus. J. Bacteriol. 184,1172-1179. 

Control by repression is referred to as negative regulation. In addition, however, where the physiology dictates, operons controlled negatively may also be under positive... 

Tal, R., Wong, H., Calhoon, R., Gelfand, D., Fear, A., Volman, G., Mayer, R., Ross, R, Amikam, D., Weinhouse, H., Cohen, A., Sapir, S., Ghana, P., Benziman, M., 1998. Three cdg operons control cellular mmover of cycUc di-GMP in Acetobacter xylinum genetic organization and occurrence of conserved domains in isoenzymes. Journal of Bacteriology 180, 4416-4425. 

The protein is believed to be a product of the lac gene nonsense mutation of that gene leads to the constitutive elaboration of these enzymes. Elaboration under the control of a gene of a protein that in fact prevented expression of the operon obviously constitutes a negative form of operon control. 

Gronewold T.M. and Kaiser D. 2001. The act operon controls the level and time of C-signal production for Myxococcus xanthus development. Mol Microbiol 40 744-756. 

Tal R, Wong HC, Calhoon R, Gelfand D, Fear AL, Volman G, Mayer R, Ross P, Amikam D, Weinhouse H, Cohen A, Sapir S, Ghana P, Benziman M (1998) Three edg operons control cellular turnover of eyelie di-GMP in Acetobacter xylinum genetic organization and occurrence of conserved domains in isoenzymes. J Bacteriol 180 4416-4425... 

Figure 3. Hierarchical levels of metabolic control. Sites of metabolic control are designated as (1) plasma membrane level active transport systems, hormone receptors (2) cytoplasmic level hormone binding protein complex, signal molecule generation (3) enzymatic level steady-state enzymatic pathway, servomechanisms, enzyme degradation (4) ribosomal level protein biosynthesis (5) nuclear level hormonal control of gene action, operon control of gene action (substrate induction, product repression). The symbol,, indicates inhibition of a reaction.

Positive regulator of a chromosomal and/or mitochondrial operon controlling the transcription of a set of genes coding for at least one component of each deficient activity cytochrome oxidase, ATPase, and X. 

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