Introduction
James F. Kane in Multifunctional Proteins: Catalytic/Structural and Regulatory, 2019
The elegant studies of Jacob and Monod1 on the lactose operon of Escherichia coli illustrated a simple yet effective means for the control of gene expression. In this system, the protein product of a regulatory gene, (i), binds to a region of the DNA called the operator locus (o). This protein prevents transcription of the structural genes of the lactose operon by the RNA polymerase that is bound to the DNA at a site called the promoter (p). This repressor protein, however, also possesses a binding site for a small molecule, namely β-allolactose. When β-allolactose binds to the repressor protein the protein-allolactose complex no longer interacts with the operator region of the DNA and the structural genes of the lactose operon are transcribed into mRNA by the RNA polymerase. This type of control is called induction and the “i” gene product is called a negative effector because it functions only in stopping synthesis of mRNA from the DNA. Subsequent studies have shown that the regulation of the lactose operon is more complex and involves cyclic AMP and a cyclic AMP binding protein.2 These latter elements are essential for the efficient transcription of the lactose operon by RNA polymerase and are, therefore, called positive regulatory elements. Despite this added level of complexity the role of the lactose repressor protein remains unchanged from the original description of its function by Jacob and Monod. That is, its sole function is the negative control, or turning off, of the transcription of the lactose operon. In this case, the regulatory gene “i” is itself constitutively expressed: that is, its expression is not regulated.3
Reactivities of Amino Acids and Proteins with Iodine
Erwin Regoeczi in Iodine-Labeled Plasma Proteins, 2019
The lactose repressor protein binds specifically to the lac operon, and prevents the tran- scription of the lac structural genes by preventing the movement of promotor-bound RNA polymerase through the operator region. This protein loses both its specific and nonspecific DNA-binding capability when Tyr-7 and Tyr-17 (both situated in the N-terminus) are mod- ified by tetranitromethane. Conversion of the affected residues to aminotyrosyls restores partial operator DNA-binding and complete nonspecific DNA-binding capability362 (See also Chapter 3, Section H.F.2.)
Introduction to Clinical Microbiology
Keith Struthers in Clinical Microbiology, 2017
The regulation of gene expression at the transcription level is central in coordinating the metabolic activity of the cell. In prokaryotic organisms such as bacteria, it is usual for all the enzymes necessary for a particular metabolic pathway to be expressed by means of one polycistronic mRNA molecule. The organization of the lactose operon of Escherichia coli, which codes for three enzymes, β-galactosidase, permease and transacetylase, is shown in Figure 1.15. All three enzymes are needed for uptake into the cell and initial processing of the carbohydrate lactose.
Regulatory mechanisms of exopolysaccharide synthesis and biofilm formation in Streptococcus mutans
Published in Journal of Oral Microbiology, 2023
Ting Zheng, Meiling Jing, Tao Gong, Jiangchuan Yan, Xiaowan Wang, Mai Xu, Xuedong Zhou, Jumei Zeng, Yuqing Li
EIIMan is the most physiologically important PTS complex in S. mutans, mainly involved in the transport of glucose, mannose, galactose, glucosamine (GlcN) and N-acetylglucosamine (GlcNAc) [74,75]. This complex is made up of four domains expressed as three polypeptides in a single operon: EIIAB (manL), EIIC (manM), and EIID (manN). Previous studies showed that the deletion of the manL gene relieved CCR of several carbohydrate catabolic operons, including the cel operon encoding a phospho-β-glucosidase (CelA), a cellobiose-PTS EII complex [76,77], the lac operon encoding EIILac (lacFE) and proteins required for the utilization of both lactose and galactose [74]. Abranches et al. found that the reduced expression of the gtfBC promoter in the EIIABMan mutant strain is associated to the involvement of ManL in the regulation of gtfBC expression [78].
Related Knowledge Centers
- Escherichia Coli
- Glucose
- Molecular Biology
- Operon
- Prokaryote
- Metabolism
- Lactose
- Gut Microbiota
- Β-Galactosidase
- Regulation of Gene Expression