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Mechanisms of Bacterial Heavy Metal Resistance and Homeostasis
Published in Edgardo R. Donati, Heavy Metals in the Environment, 2018
Pallavee Srivastava, Meenal Kowshik
The expression of genes encoding metallochaperones, metal importers, and exporters is controlled by a panel of specialized transcriptional regulators known as metalloregulatory proteins or “metal sensor” proteins. In prokaryotes, the cellular response to perturbations in metal homeostasis is nearly exclusively transcriptional. The transcriptional response elicited by these metalloregulatory proteins depends on the intracellular metal activity or free metal concentration that dictates the activation or the inhibition of the downstream genes (Outten and O’Halloran, 2001). The metal mediated repression or derepression of a metal uptake or efflux gene depends on the kind of allosteric regulation exhibited by the metal sensor protein. In most of the instances, the transcriptional repressor binds to a specific DNA operator blocking the binding of RNA polymerase subsequently preventing the transcription of the gene (Cavet et al., 2002). An exception to this rule is exhibited by the MerR-family of regulators, where both the RNA polymerase and the metal bound MerR family member are bound simultaneously to the promoter, thereby activating the transcription of the efflux transporters (Outten et al., 1999). Thus, MerR family are transcriptional activators; ArsR/SmtB, CopY, and CsoR/RcnR families are transcriptional de-repressors; and the Fur, DtxR, and NikR families are the transcriptional co-repressors (Table 1).
Processes for Overproduction of Microbial Metabolites for Industrial Applications
Published in Nduka Okafor, Benedict C. Okeke, Modern Industrial Microbiology and Biotechnology, 2017
Nduka Okafor, Benedict C. Okeke
Whereas feedback inhibition results in the reduction of the activity of an already synthesized enzyme, feedback repression deals with a reduction in the rate of synthesis of the enzymes. In enzymes that are affected by feedback repression, the regulator gene (R) is said to produce a protein aporepressor which is inactive until it is attached to corepressor, which is the end-product of the biosynthetic pathway. The activated repressor protein then interacts with the operator gene (O) and prevents transcription of the structural genes (S) on to mRNA. A derivative of the end-product may also bring about feedback repression. It is particularly active in stopping the overproduction of vitamins which are required only in small amounts (see Fig. 6.1).
General Introductory Topics
Published in Vadim Backman, Adam Wax, Hao F. Zhang, A Laboratory Manual in Biophotonics, 2018
Vadim Backman, Adam Wax, Hao F. Zhang
Transcription factors are DNA-binding proteins. Some DNA-binding proteins are activators, while others are repressors. Their names tell it all: Activators increase the rate of gene transcription, while repressors do the opposite. These factors are critically important in transcription, as without their help, only a very low level of transcriptional activity would be possible. Other modulator molecules include coactivators—proteins that assist transcription factors to increase the rate of gene transcription—and corepressors—proteins that work with transcription factors to decrease the rate of transcription.
New strategies for treatment of COVID-19 and evolution of SARS-CoV-2 according to biodiversity and evolution theory
Published in Egyptian Journal of Basic and Applied Sciences, 2020
The microRNA is not only present in all living organisms, but also, in some viruses which used it in controlling of host cells. The discovery of RNA interference and cellular microRNA has not only affected how biological research is conducted but also revealed an entirely new level of posttranscriptional gene regulation. The potential functions of the virally encoded miRNAs were identified in several pathogenic human viruses. Cellular miRNAs may have had a substantial effect on viral evolution and may continue to influence the in vivo tissue tropism of viruses [18]. Every herpesvirus that has been analyzed encodes several viral miRNAs, and the other viruses that have so far been shown to encode a single miRNA (i.e., simian virus 40 (SV40) and adenovirus) are also nuclear DNA viruses [19,20]. In contrast, the RNA viruses such as the fever virus, human immunodeficiency virus and hepatitis C virus (HCV) do not seem to encode any miRNAs 27. Viruses are obligatory intracellular parasites that rely on a wide range of cellular factors to successfully accomplish their infectious cycle. Among those, microRNAs have recently emerged as important modulators of viral infections. These small regulatory molecules act as repressors of gene expression. During infection, miRNAs can function by targeting cellular RNAs [21]. It has been observed that pathogens and some viruses that contain microRNA can induce the up-/down regulation of various host miRNAs in order to evade the host’s immune system. In contrast, some miRNAs studied could have an antiviral effect, enabling the defense mechanisms to fight the infection or, at the very least, they could induce the pathogen to enter a latent state. At the same time, some viruses encode their own miRNAs, which could further modulate the host’s signaling pathways, thus favoring the survival and replication of the virus. The clinical applications of miRNAs are extremely important, as miRNAs targeted inhibition may have substantial therapeutic impact. Inhibition effect of miRNAs can be achieved through many different methods, but chemically modified antisense oligonucleotides have shown the most prominent effects [22].