Extrachromosomal plasmids

Figure 1 Strategy for tailoring the stereoselectivity of whole-cell baker s yeast-mediated reductions. The level of a yeast reductase can be increased by placing the corresponding gene under control of a strong yeast promoter on an extrachromosomal plasmid. Alternatively, the catalytic activity of a reductase can be eliminated by replacing the corresponding gene on the chromosome with a defective copy prepared in vitro. (Reprinted with permission from Organic Letters 1999, 1. 1999 American Chemical Society.)...

Plasmid pVTL2, which is another example of an extrachromosomal plasmid [83], was used to express the firefly luciferase gene under the control of various promoters. The luciferase gene can be replaced for other heterologous transgenes, which can be expressed from any D. discoideum promoter introduced into the multiple cloning site. The pVTL2 plasmid was reported to produce 10-50 copies per cell [83]. 

Plasmid DNAs. Plasmids are nucleic acid molecules capable of intracellular extrachromosomal repHcation. Usually plasmids are circular DNA species, but linear and RNA plasmids are known. In nature, plasmids can assume a variety of lifestyles. Plasmids can recombine into the host chromosome, be packaged into vims particles, and repHcate at high or low copy number relative to the host chromosome. Additionally, their information can affect the host phenotype. Whereas no single plasmid is usually capable of all these behaviors, the properties of various plasmids have been used to constmct vectors for a variety of purposes. 

Plasmid A small, extrachromosomal, circular molecule of DNA that rephcates independendy of the host DNA. 

Plasmids and DNA Repair. Plasmids are extrachromosomal genetic elements that are composed of circular double-stranded DNA. In bacteria some can mediate their own transfer from cell to cell by conjugation they contain a set of Ira genes coding for tube-like structures, such as pili, through which a copy of plasmid DNA can pass during transfer. Plasmids range in size from 1.5 to 200 million daltons. The number... 

Long-term, low-level feeding of penicillin and the tetracyclines promotes, by natural selection from the pool of normal intestinal flora, those enteric (gut) bacteria that contain R-plasmids. R-plasmids, also known as R-factors, are extrachromosomal genetic material which confer antibiotic resistance to host bacteria. These plamids can be transferred between various kinds of bacteria through cell-to-cell contact (conjugation). Simultaneous resistance to several unrelated antibiotics is commonly carried on a single plasmid and therefore is simultaneously transferred from one bacterium to another. 

Plasmid A small extrachromosomal cicular DNA molecule capable of reproducing independently in a host, prokaryote, or eukaryote, cell... 

Definition of a plasmid Function in amplification of DNA Prokaryotic organisms normally contain small, circular, extrachromosomal DNA molecules called plasmids that can serve as vectors. They can be readily isolated from the bacterium, annealed with the DNA of interest, and reintroduced into the bacterium which will replicate, thus making multiple copies of the hybrid plasmid. 

The small pieces of DNA known as plasmids, which replicate independently of the chromosomes, have been discussed briefly in Chapter 5. Plasmids share a number of properties with viruses, and both are important to the techniques of contemporary molecular biology and genetic engineering. Bacterial plasmids may be present as one or several copies for each chromosome. Episomes are plasmids that are able to become integrated into the bacterial chromosome. Some extrachromosomal elements are episomes in one host and plasmids in another. Bacterial... 

Extrachromosomal DNA molecules called plasmids are harbored in some strains of E. coli. The normal copy number of the plasmids is small, between 2 and 10 however, if these strains of E. coli are grown in the presence of chloramphenicol, up to 3000 copies may be replicated per cell. Plasmid DNA has been demonstrated to be a useful vehicle in molecular cloning. This experiment describes a method for the growth of E. coli and amplification of the ColEl plasmids. The plasmids will be isolated from E. coli cells by one of two methods, a large-scale boiling method or a microscale alkaline lysis method. The DNA plasmids will be measured for molecular size by agarose electrophoresis. 

Many bacterial cells contain self-replicating, extrachromosomal DNA molecules called plasmids. This form of DNA is closed circular, double-stranded, and much smaller than chromosomal DNA its molecular weight ranges from 2 X 106 to 20 X 106, which corresponds to between 3000 and 30,000 base pairs. Bacterial plasmids normally contain genetic information for the translation of proteins that confer a specialized and sometimes protective characteristic (phenotype) on the organism. Examples of these characteristics are enzyme systems necessary for the production of antibiotics, enzymes that degrade antibiotics, and enzymes for the production of toxins. Plasmids are replicated in the cell by one of two possible modes. Stringent replicated plasmids are present in only a few copies and relaxed replicated plasmids are present in many copies, sometimes up to 200. In addition, some relaxed plasmids continue to be produced even after the antibiotic chloramphenicol is used to inhibit chromosomal DNA synthesis in the host cell. Under these conditions, many copies of the plasmid DNA may be produced (up to 2000 or 3000) and may accumulate to 30 to 40°/o of the total cellular DNA. 

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