Selection Marker antibiotic

The dimension of an antibody library, typically defined as the number of clones bearing a suitable selectable marker (antibiotic resistance) and, containing the full-size antibody gene (detectable by PCR screening 32), does not necessarily correspond to the functional dimension of a library, which requires that the clones express properly folded antibodies. An approximation for the determination of the functional dimension of a library consists of determining what percentage of clones expresses antibodies, for example, using immunoblot techniques. 

D. J. Drahos, B. C. Hemming, and S. McPherson, Tracking recombinant organisms in the environment P-galactosida.se as a selectable non-antibiotic marker for fluorescent psudeomonads. Biotechnology. 4 439 (1986). 

DNA construct will often contain an effect gene and a selectable marker gene (such as antibiotic or herbicide resistance), both of which are bracketed by promoter and terminator sequences. A plasmid vector carries this cassette of genetic information into the plant genome by one of the above methods. 

Technically, cDNAs are cloned into plasmids carrying an antibiotic selection marker for propagation in bacteria, a nutritional selection marker for selection of transfected yeast as well as the respective origins of replication. After amplification in bacteria, the plasmids are transfected into the corresponding auxothrophic yeast strain using similar methods as for bacteria and stably... 

Although not as popular as the baculovirus-system, stable transformations of insect cells can be used to circumvent the problems mentioned in the last paragraph. Common hosts include the fruitfly and mosquito. The expressed genes are often under the control of the Drosophila metallothionein promoter. Genes coding for resistance to antibiotics such as hygromycin and neomycin are used as selection markers. 

Herrero, M., de Lorenzo, V. Timmis, K. N. (1990). Transposon vectors containing non-antibiotic resistance selection markers for cloning and stable chromosomal insertion of foreign genes in gram-negative bacteria.Journal of Bacteriology, 172,6557-67. 

The plasmid should contain identifiable markers so that it is possible to screen progeny for the presence of the plasmid. At least two selective markers are desirable, a primary one to confirm the presence of the plasmid and a secondary marker to confirm the insertion of foreign DNA. Resistance to antibiotics is a convenient type of marker. 

Another major application of herbicide resistance is its utility as a selectable marker. Like antibiotic resistance in bacterial transformation, herbicide resistance should prove extremely useful for selecting transformants that are insect resistant, disease resistant, or engineered for other non-selectable traits. Many of these herbicide resistant markers have already been integrated into plant cloning vectors (32.43). 

Over several decades, multiple vector systems for recombinant gene expression in E. coli have been developed. Modem vectors suitable for recombinant protein production vary in the used promoter system in the presence or absence of coding sequences for affinity tags upstream or downstream of the multiple cloning site (MCS) and of sequences coding for leader peptides for the protein export. Moreover, different origins of replication (ori), antibiotic selection marker genes and MCS are used. 

The second component of an expression vector comprises DNA sequences required for the selection, maintenance and copy-number amplification of the vector in the host cell wherein protein expression is desired. Obviously, this region is not needed for expression in E. coli. The selectable markers used in other host cells may be an enzyme conferring the ability to produce a nutrient essential for growth of the host cell, or transformation of cell morphology, or resistance to antibiotics (such as hygromycin or geneticin). Sequences for the maintenance of the vector DNA are required for the autonomous replication of the plasmid in these host cells except in cases where the vector sequences Tntegrate into chromosomes of the... 

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