Promoter regions operons

Fig. 5.39. The control of enzyme synthesis by catabolite repression. A control region of the lac operon contains the CAP binding site within the promoter region...

Promoter region of the nar operon, which encodes nitrate reductase in Escherichia coli. The promoter is generally only maximally induced under anaerobic conditions. It has been shown that the nar promoter in some strains of Escherichia coli can be induced under conditions of very low oxygen tension in the presence of nitrate. This observation has been used to develop some useful processes for recombinant protein expression in Escherichia coli. See Li, S.F. and DeMoss, J.A., Promoter region of the nar operon of Escherichia coli nucleotide sequence and transcription initiation signals, J. Bacteriol. 169, 4614- 620, 1987 Han, S.J., Chang,... 

Operons contain promoter regions where proteins bind and facilitate or inhibit the binding of RNA polymerase. 

B. cAMP is involved in catabolite repression. Bacterial cells preferentially use glucose. When glucose is low, cAMP rises. cAMP binds to a protein and complexes near the lac promoter region, facilitating binding of RNA polymerase. Lactose must be present to inactivate the repressor, so that the operon may be expressed. 

Some proteins activate transcription by directly contacting RNA polymerase. For example, cyclic AMP, a hunger signal, stimulates the transcription of many catabolic operons by binding to the catabolite activator protein. The binding of the cAMP—CAP complex to a specific site in the promoter region of an inducible catabolic operon enhances the binding of RNA polymerase and the initiation of transcription. 

The formation of avermectin aglycons involves KRs that resemble type I and II FAS. The C5-keto group is reduced by a monofunctional KR (AveF) that is not within module 11 of the AVES 4 (Fig. 10). The mutants defective in C5 ketore-ductase gene, aveF, which were obtained by introducing an insertion mutation in the promoter region of aveD-aveF operon produced 5-oxoavermectins [104]. 

Li S E, DeMoss J A (1987). Promoter region of the nar operon of Escherichia coli Nucleotide sequence and transcription initiation signals. J. Bacteriol. 169 4614-4620. 

CAP is a positive control element. When the level of glucose in cells is low, the level of cAMP is high, leading to the formation of cAMP-CAP complex. The cAMP-CAP complex binds to DNA in the promoter region, creating an entry site for RNA polymerase. The result is the transcription of the lactose operon (providing that no repressor is present) (see Figure 31.10 on p. 873 of the text). Coactivators act as positive control elements in eukaryotic transcription (see pp. 881-882 in the text). 

Pribnow box A consensus sequence of nucleotides - TATAAT - occurring in the promoter region of prokaryote genes see operon) about 10 nucleotides before the start of transcription. The predominance of adenine and thymine bases means that hydrogen bonding between the two DNA strands in this region is relatively weak, enabling the strands to be separated more easily to permit transcription by RNA polymerase. See also TATA box. 

FIGURE 4. Alignment of puf operon promoter sequences with proposed promoter sequences from the bchCA operon. Numbers of the first and last nucleotides of these sequences correspond to the sequence positions given for the pu/operon promoter region (7), and of the bchCA operon promoter region (Fig. 2). Identical sequences are boxed, and the nucleotides from which transcription is proposed to be initiated are marked by arrows. 

Bauer, C.E., Young, D.A., and Marrs, B.L. (1988) Analysis of the Rhodobacter capsulatus puf operon. Location of the oxygen-regulated promoter region and the identification of an additional p /-encoded gene. J. Biol. Chem. 263,4820-4827. 

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