Eukaryotic cells gene expression

Gene expression in human cells is regulated primarily at the level of transcription as it is in prokaryotic cells. However, because transcription is more complex in eukaryotic cells, gene expression can be regulated at many different... 

There exist a variety of vectors for cloning into eukaryotic systems, ranging from yeast (Saccharomyces as well as Pichia) through insect cells (Baculovims) and plants (Ti plasmid from Agrobacterium tumefaciens) to mammalian cells (transfected by viral or mammalian vectors). As expression in eukaryotic hosts is less efficient than bacterial expression in terms of yield and time and more complicated in terms of vector structure and culture conditions, such eukaryotic expression systems are only used for genes whose proteins require posttranslational modification which is not possible in bacteria. Yeast is the preferred option as a relatively easily culturable single-cell system but posttranslational modification capabilities is limited. The additional complexity can be circumvented in part by exploiting the ability of eukaryotic vectors to act as shuttle vectors, which can be shuttled between two evolutionarily different hosts. Thus, eukaryotic vectors can be replicated and analyzed in bacteria and transfected into eukaryotic cells for expression of the recombinant product. 

Berger J, Hauber J, Hauber R, Geiger R, Cullen BR (1988), Secreted placental alkaline phosphatase a powerful new quantitative indicator of gene expression in eukaryotic cells, Gene 66 1-10. 

Papas, T.S.l Rosenberg, M. Chirikjian, J.G. (Eds.) Expression of Cloned Genes in Prokaryotic and Eukaryotic Cells", GENE AMPLIFICATION AND ANALYSIS Vol. 3 Elsevier New York, 1983, 286 pp. 

Kessel, M., and Khoury, G., 1983, Induction of cloned genes after transfer into eukaryotic cells, in Expression of Cloned Genes in Prokaryotic and Eukaryotic Cells, Vol. 3, (T. S. Papas, M. Rosenberg, and J. G. Chirikjian, eds.), pp. 233-260, Elsevier, New York. 

The eukaryotic expression cassette is the part of an expression vector that enables production of a protein in a eukaryotic cell. The cassette consists of a eukaryotic promoter for mRNA transcription, the gene and an mRNA termination and processing signal (Poly-A signal). 

Heterologous expression systems comprise prokaryotic organisms (e.g., E. coli) and eukaryotic cells (e.g., yeast, HEK293, Xenopus oocytes), which are used to functionally express foreign genes or cDNAs. 

Li, G. Laszio, A. (1985). Thermotolerance in mammalian cells A possible role for the heat shock proteins. In Changes in Eukaryotic Gene Expression in Response to Environmental Stress (Atkinson, B.G. Walden, D.B. eds.), pp. 349-371, Academic Press, Orlando. 

Table 39-4. Gene expression is regulated by transcription and in numerous other ways in eukaryotic cells.

In addition to affecting the efficiency of promoter utilization, eukaryotic cells employ alternative RNA processing to control gene expression. This can result when alternative promoters, intron-exon splice sites, or polyadenylation sites are used. Occasionally, heterogeneity within a cell results, but more commonly the same primary transcript is processed differendy in different tissues. A few examples of each of these types of regulation are presented below. 

In the nuclei of all eukaryotic cells, DNA is tightly wrapped around an octamer of histone proteins and is compacted into a dense structure known as chromatin. In order to access the genetic information which is required in numerous essential cellular processes including DNA replication, gene expression and DNA repair, chromatin needs to be partially unwound. One important mechanism to regulate chromatin structure and thus to control the access of the genomic DNA is through histone modifications [1-6]. The histone octamer is composed of two copies of H2A, H2B, H3 and H4 core histone proteins. Their tails, that protrude out of the surface of the... 

Smirnova, J. B., Selley, J. N., Sanchez-Cabo, F., Carroll, K., Eddy, A. A., McCarthy, J. E., Hubbard, S. J., Pavitt, G. D., Grant, C. M., and Ashe, M. P. (2005). Global gene expression profiling reveals widespread yet distinctive translational responses to different eukaryotic translation initiation factor 2B-targeting stress pathways. Mol. Cell Biol. 25, 9340-9349. 

DNA plasmid-based treatment ( gene therapy ) is considered an alternative to the one based on classical chemical drugs or proteins recovered from recombinant cells. Treatment of acquired and inherent genetic diseases as well as the use of DNA for the purpose of vaccination are potential applications of plasmid DNA (pDNA). The plasmid carries information that allows protein expression in the targeted human cells as well as eukaryotic regulatory elements and specific prokaryotic sequences that control replication in the host cell, see Fig. 10. Formulation is required for ex- or in-vivo administration. Selected systems for gene expression can be viral or non-viral. 

The concept of the cell cycle (Figure 1-1-2) can be used to describe the timing of some of these events in a eukaryotic cell. The M phase (mitosis) is the time in which the cell divides to form two daughter cells. Interphase is the term used to describe the time between two cell divisions or mitoses. Gene expression occurs throughout all stages of interphase. Interphase is subdivided as follows ... 

Table 1-5-2 summarizes some of the mechanisms that control gene expression in eukaryotic cells. 

If the end goal of cloning is to have a cloned gene expressed in a cell, the entire coding sequence must be doned intact. Furthermore, if a cloned eukaryotic gene is to be expressed in bacteria (to make recombinant proteins), the gene must not contain introns, which could not be processed in a prokaryotic cell. In these cases it is more convenient to done cDNA rather than DNA restriction fragments. 

Kato, N., Brooks, W. and Calvo, A.M., Sterigmatocystin and penicillin pene expression is controlled by veA, a gene required for sexual development in Aspergillus nidulans. Eukaryotic Cell, in press. 

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