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Human physiology, hazards and health risks
Published in Stephen Battersby, Clay's Handbook of Environmental Health, 2023
Revati Phalkey, Naima Bradley, Alec Dobney, Virginia Murray, John O’Hagan, Mutahir Ahmad, Darren Addison, Tracy Gooding, Timothy W Gant, Emma L Marczylo, Caryn L Cox
For a second reason why epigenetics matters let’s go back to biological sex again. All the gametes from the mother will carry an X chromosome but that from the father will carry an X or Y. The sex chromosome from the father that ends up in the zygote will therefore define biological sex, X for a female and Y for a male. Now consider gene dosage. The best way of thinking about this is to consider a disease where gene dosage is abnormal, and for the purposes of this chapter we can consider Down’s syndrome as an example. In the common form of Down’s syndrome there is an additional copy of chromosome 21, so there are three copies. This means there is differential expression of some genes encoded or controlled by genes on chromosome 21, leading to the characteristic phenotype [7]. Returning to the X chromosome, why is it then that females do not have a gene dosage effect from their additional X chromosome compared to males that have only one X chromosome but are equally dependent on the X chromosome genes? The answer lies in epigenetics. Within each cell of a female one copy of the X chromosome is turned off through the process of epigenetic X chromosome inactivation. This suppression is random so that in any one cell of a female the X chromosome from either the father or the mother is inactivated via DNA methylation [8].
Serratia marcescens
Published in Yoshikatsu Murooka, Tadayuki Imanaka, Recombinant Microbes for Industrial and Agricultural Applications, 2020
When pSK301 was introduced into S. marcescens strains, these enzymatic activities were increased about fivefold, and the copy number was five to six per chromosome. The gene dosage effect of this recombinant plasmid on threonine production was studied. When D-60, wild-type, was used as a host, pSK301 provided cells with 15 g of l-threonine production (Table 2). The introduction of pSK301 into strain T-1112 (thrA¡5 ThrA2 hnrAl) increased the production from 8 to 35 g/L. Strain T-l 165 was constructed by transductional crosses, as described for T-1026, and the seven regulatory mutations, including the thr A ¡5 and thr A 25 mutations, and produced l-threonine at 44 g/L. When pSK301 was introducted into T-l 165, the recombinant strain, T-2000, produced 60 g/L of this amino acid in a shake flask. This production was no higher than expected and, therefore, culture conditions were studied using ajar fermentor, as will be described later (see Sec. D).
Selection and Improvement of Industrial Organisms for Biotechnological Applications
Published in Nduka Okafor, Benedict C. Okeke, Modern Industrial Microbiology and Biotechnology, 2017
Nduka Okafor, Benedict C. Okeke
Two important features of plasmids to be used in genetic experiments may be compared by examining two plasmids. Plasmid psC101 has only two to five copies per cell and replicates with its host DNA. It is said to be under ‘stringent’ control. However, another plasmid pCol E 1 is found in about 25–30 copies per cell. It has a ‘relaxed control’ independent of the host and replicates without reference to the host DNA. When the host cell is starved of amino-acids or its protein synthesis is inhibited in some other manner, such as with the use of chloramphenicol, the Col E 1 plasmid continues to replicate for several hours until there are 1,000 to 3,000 copies per cell. Due to this high level of gene dosage (also referred to as gene amplification), products synthesized because of the presence of these plasmids are produced in extremely high amounts, a property of immense importance in biotechnology and industrial microbiology. Generally, conjugative plasmids are large, exhibit stringent control of DNA replication and are present in low copy numbers; on the other hand, non-conjugative plasmids are small, show relaxed DNA replication, and are present in high numbers (Table 7.5).
Bioprocessing of recombinant proteins from Escherichia coli inclusion bodies: insights from structure-function relationship for novel applications
Published in Preparative Biochemistry & Biotechnology, 2023
Kajal Kachhawaha, Santanu Singh, Khyati Joshi, Priyanka Nain, Sumit K. Singh
Plasmids are the most common vectors utilized in recombinant DNA technology. Properties such as its size, copy number and promotor strength significantly contribute to the recombinant protein production in the host cell. The recombinant gene dosage is defined by the copy number of the plasmid. High gene dosage can either be favorable or unfavorable for the expression of the recombinant protein. Thus, a suitable plasmid should be selected, keeping it mind the characteristics it possesses.[56,57] To achieve a higher recombinant protein expression, the interest gene should be cloned immediately downstream to a strong promoter.[58] Strong transcriptional promoters control the foreign gene in various plasmids and bacteriophage vectors.[58] These promoters do not show constitutive expression and are governed by adding specific metabolites or changing culture conditions.[59] These are highly regulated in nature and also control the expression of the foreign gene in such a way that they do not interfere with the normal functioning of cellular genes and are not toxic to the host cell.[60] If these promoters are not regulated, they may result in loss of plasmid carrying the strong promoter or may be expressed constitutively, which shows detrimental effects on the cell.[59] The tae promotor is the most commonly used strong promotor.[58]