Lac control region

Nucleotide sequence of the lac control region 1638 9. Conformational Properties of RNA... 

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...

Different genetic elements of the lac operon. The operon contains a control region, the promoter-operator region, and three structural genes, z, y, and a. The i gene, a repressor, is also shown. It is not part of the operon, but it is located at an adjacent site on the genome with its own promoter. 

HEK-293 hGH High-Five hsp70 HSV IPTG IRES kb Lac LCR LoxP LUC MCS human embryonic kidney cells human growth hormone TM BTI-TN-5B1-4 (cell line derived from the insect Trichoplusia ni) heat shock protein 70 herpes simplex virus isopropyl 1 -thio-fi-D-galactopyranoside internal ribosomal entry site kilobases lactose operon/repressor locus control region locus of crossover of PI luciferase isolated from firefly multiple cloning site... 

Figure 23. An inverted sequence repair in the control region of the lac gene.

The organism senses whether glucose is available by another regulatory mechanism which cooperates with the lac repressor and the lac operator. The promoter is therefore sub-divided into two specific regions, each of distinctive function. One is the RNA polymerase entry site, where RNA polymerase first becomes bound to DNA (cf. DNA transcription, Appendix 5.6), and the other is the protein binding site for the catabolite activator protein (CAP) (Fig. 5.39). The CAP protein binding site controls the polymerase site which, when bound to the DNA, allows successful transcription provided that the repressor is not bound. When the CAP protein is not bound, then RNA polymerase cannot bind and transcription cannot take place. 

Both H- and L-NHase genes are expressed under the control of a lac promoter in E. coli only when the transformants are cultured in the presence of CoCl2 [63], However, the level of NHase activity in their cell-free extracts is much lower than those of H- and L-NHases in R. rhodochrous Jl. Most of H-NHase is produced as an insoluble form in the E. coli transformant, and there is only a little L-NHase in either the supernatants or precipitates of the extracts. Establishment of an effective host-vector system in Rhodococcus [71] facilitates the development of strains with improved NHase activities. In this connection, the transformation system in Rhodococcus has been investigated. Enzyme assays of recombinant Rhodococcus cells showed that a downstream region of the Rhodococcus sp. N-774 NHase gene is indispensable for the production of active... 

Eukaryotic genes may be clustered (for example, genes for a metabolic pathway may occur on the same region of a chromosome) but are independently controlled. Operons or polycistronic mRNAs do not exist in eukaryotes. This contrasts with prokaryotic genes, where a single control gene often acts on a whole cluster (for example, lac I controls the synthesis of p-galactosidase, permease, and acetylase). 

The physiological signal controlling the lac and ara operons is the utilization of carbon sources for metabolic energy. In contrast, the tryptophan trp) operon is sensitive to the need for biosynthetic processes and is transcribed under conditions where intracellular concentrations of the amino acid tryptophan are below an optimal level for efficient protein synthesis. The trp operon consists of a promoter and operator region which controls the expression of a polycistronic mRNA encoding five proteins needed for tryptophan biosynthesis. 

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