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Genetics and Mutants
Published in Paul Pumpens, 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).
Homology of Nonrepeated DNA Sequences in Phylogeny of Fungal Species
Published in S. K. Dutta, DNA Systematics, 2019
As shown in the affinity diagram (Figure 3), the average sequence homology between the two parental types (75%) was lower than their hybrids (85 to 88%). The dissimilarities between the parental types could account for the polarity difference in sexual positioning, female gametangial morphology, and the intensity of carotenoid pigmentation in the male gametangia. The male and female strains hybridized to an equal extent with their parental types and had lower sequence dissimilarity (see Figure 3). These results provide molecular proof of the earlier conclusions drawn by Emerson and Wilson70 that these strains are true hybrids. These results also indicate that the male strains share more sequences in common with the parental types than the female strains; however, the hybrid duplexes from male strains contain more divergent base pairs than the female strains.37 A comparison of the ribosomal RNA cistron number in the hybrid strains has shown that the male strain has about 60% deletion of RNA cistrons as compared to the wild type and the female.71 The fact that laboratory-derived stable strains with significant sequence divergence can be produced by sexual crossings poses some problem in the traditional estimation of absolute time based sequence divergence in evolution, since such interspecific mating may occur in nature and one can then find new species through genetic recombination and not through the accumulation of mutation which is a longer process.
Escherichia Coli Ribosomal Proteins Involved in Autogenous Regulation of Translation
Published in James F. Kane, 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.
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.