Cascade Regulation a Model of Integrative Control of Gene Expression in Eukaryotic Cells and Organisms
M. Gerald, M.D. Kolodny in Eukaryotic Gene Regulation, 2018
Genes — Confronted with the relativation of terms such as “gene” and “cistron”,78 we define, for the purpose of this chapter, genes in their old-fashioned sense — but compatible with modern concepts — as the unit of information assignable to an individual polypeptide chain, as the functional unit of activity underlying the phenotypic expression of a genetic character. The full-length mRNA and the corresponding polypeptide represent, hence, the physical and biochemical correlates of a “gene”. In many cases, genes are stored in the DNA in fragmented form (cf. gene dispersion). By this definition, pleiotropic signals of regulation and processing, e.g., service signals, operating at pre-mRNA level but eliminated from mRNA, are excluded from the gene as from an individual genetic character.
Escherichia Coli Ribosomal Proteins Involved in Autogenous Regulation of Translation
James F. Kane in Multifunctional Proteins: Catalytic/Structural and Regulatory, 2019
An alternative model for the expression of ribosomal proteins within translational regulatory units is that translation of each cistron can be initiated by free ribosomes: but, the initiation at second and more distal cistrons depends on the translation a certain distance into the preceeding cistron, which is required to disrupt secondary or tertiary mRNA structures that otherwise prevent access of ribosomes to the initiation sites. Independent initiation would only occur at the start site of the first cistron of the regulatory unit. The ratio of proteins synthesized in the regulatory unit would depend on the relative strengths of initiation signals at the different translation start sites on the polycistronic mRNA. Such a model could be required to account for regulation of L7/L12 synthesis by L10. L10 translationally represses the synthesis of both L10 and L7/L12, the products of the first and second genes, respectively, of the β operon (see Figure 1). Yet while ribosomes contain a single copy of L10 (like almost all other ribosomal proteins), they contain four copies of L7/L12.28,29 In vitro experiments demonstrate that the L10 target site is at the beginning of the L10 gene and that there is no independent site for repressor action near the L7/L12 gene.16 The results imply that translation of L7/L12 mRNA, though at least four times as efficient as translation of L10 mRNA, is nevertheless dependent upon translation of the preceeding L10 mRNA.
Genetics and Mutants
Paul Pumpens in Single-Stranded RNA Phages, 2020
The situation changed cardinally with the introduction of two general classes of the conditionally lethal mutants: the temperature-sensitive (ts) mutants and the host-dependent (amber) mutants (Luria 1962; Epstein et al. 1963). By the classical review of Norton D. Zinder (1965) on the newly appearing conditionally lethal mutants with respect to the RNA phages,the advantage of such mutants is that they should be obtained in all cistrons without necessarily any knowledge of cistron function. Any gene which is responsible for the production of protein might mutate to produce a protein with a lower thermostability than that produced by the wild type. Host-dependent mutants depend on the presence in the bacteria of specific suppressor genes which relate to particular code words rather than to specific functions. These suppressor genes are assumed to modify some aspect of the protein synthesizing mechanism in such a way that a code word which is uninterpretable in the normal host (nonpermissive) can be interpreted in the mutant host (permissive).
Construction of bicistronic cassette for co-expressing hepatitis B surface antigen and mouse granulocyte-macrophage colony stimulating factor as adjuvant in tobacco plant
Published in Pharmaceutical Biology, 2019
Sara Mohammadzadeh, Hamideh Ofoghi, Mina Ebrahimi-Rad, Parastoo Ehsani
Therefore, transient expression systems show several applications in research such as comparative analysis of plant promoters and regulatory elements, quick production of protein of interest for verification of the stability and functionality of plant produced recombinant proteins. Moreover, it is deduced that the secondary structure of the mRNA of the whole construct affects the second cistron using TEV-based cassettes.
Successful production of human epidermal growth factor in tobacco chloroplasts in a biologically active conformation
Published in Growth Factors, 2023
Yunpeng Wang, Jieying Fan, Niaz Ahmad, Wen Xin, Zhengyi Wei, Shaochen Xing
Although the expression of hEGF has been achieved in many plant species, the expression/accumulation levels varied greatly in these reports, even when the same plant species was used as a host. It could be due to different expression strategies adopted, which might led to these variations. Researchs show that higher plant chloroplasts are capable of expressing foreign proteins at quite high levels. For instance, 37% TSP of His6-MBP (Ahmad et al. 2012), more than 70%TSP of PlyGBS (Oey et al. 2009), 72.0% TSP of CTB-Pins (Ruhlman et al. 2010), and more than 75% TSP of β‑glucosidase (Feng et al. 2020). The expression levels for hEGF in earlier report using chloroplast transformation approach were also quite low (0.001% TSP)(Wirth et al. 2006); the higher expression obtained in this study might be due to dual strong fusion promoters, PrrnPclpPrbcL (Kittiwongwattana et al. 2007), which involved the leader of ClpP gene and the ribosomal binding site of rbcL gene, used to drive the expression of hEGF (Figures 1 and 2), as the mRNA could confer higher translation efficiency (Yu et al. 2020). On the other hand, in polycistronic expression cassette, the genes downstream often show poorer mRNA stability and lower translation efficiency (Zhou, Karcher, and Bock 2007), this may be one of the reason for low expression of EGF (EGF was downstream of aadA in the same cistron) in earlier study (Wirth et al. 2006). In this study, the foreign hEGF expression cassette is monocistronic, which might have contributed to higher transcription and translation as well as production of more stable transcripts. Expression levels might be improved further by using different set of untranslated regions (UTRs). In higher plant chloroplasts, expression is highly regulated at the post-transcriptional level. Therefore, the use of different UTRs might result in improved expressions. For example, accumulation of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) in tobacco chloroplasts was 10,000 fold increased by simply using a different set of 5′-UTRs (Ye et al. 2001).