Plasmids properties

Chromatography is relatively easy to optimize and scale up, and several plasmid properties, such as charge and size, can be exploited in the design of these separations. Typically, plasmid DNA of 3000-base pair (bp) size has an average length of 10,050 A (based on 3.35 A/bp). However, upon super-coiling, plasmids adopt a branched interwined shape and become more... 

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. 

Most plasmids are topologically closed circles of DNA. They can be separated from the bulk of the chromosomal DNA by virtue of their resistance to alkaline solution. The double-stranded stmcture of DNA is denatured at high pH, but because the two strands of the plasmid are topologically joined they are more readily renatured. This property is exploited in rapid procedures for the isolation of plasmid DNA from recombinant microorganisms (5,6). 

Over 4 decades, between 1960 and 2000, the development of new antibiotics used well characterized basic structures for partial synthetic modifications, primarily to overcome resistance by increasing the pharmacodynamic properties and, secondarily, to improve the pharmacokinetic profile of older compounds. However, bacteria rapidly responded by acquiring additional genetic alterations either as mutations or by accumulating resistance genes as part of mobile genetic elements ( integrons) on transferable resistance plasmids. 

Bacterial plasmids are small, circular, duplex DNA molecules whose natural function is to confer antibiotic resistance to the host cell. Plasmids have several properties that make them extremely useful as cloning vectors. They exist as single or multiple copies within the bacterium and replicate independently from the bacterial DNA. The complete DNA sequence of many plasmids is known hence, the precise location of restriction enzyme... 

Plasmids have the ability to transfer within and between species and can therefore be acquired from other bacteria as well as a consequence of cell division. This property makes plasmid-acquired resistance much more threatening in terms ofthe spread of antibiotic resistance than resistance acquired due to chromosomal mutation. Plasmids also harbour transposons (section 2.1.3), which enhances their ability to transfer antibiotic resistance genes. 

Plasmid- ortransposon-encoded chloramphenicol acetyltransferases (CATs) are responsible for resistance by inactivating the antibiotic. CATs convert chloramphenicol to an acetoxy derivative which fails to bind to the ribosomal target. Several CATs have been characterized and found to differ in properties such as elecfrophorefic mobilify and cafalyfic acfivify. 

Bacterial resistance to biocides (Table 13.2) is usually considered as being of two types (a) intrinsic (innate, natural), a natural property of an organism, or (b) acquired, either by chromosomal mutation or by the acquisition of plasmids or transposons. Intrinsic resistance to biocides is usually demonstrated by Gram-negative bacteria, mycobacteria and bacterial spores whereas acquired resistance can result by mutation or, more frequently, by the acquisition of genetic elements, e.g. plasmid- (or transposon-) mediated resistance to mercury compounds. Intrinsic resistance may also be exemplified by physiological (phenotypic) adaptation, a classical example of which is biofilm production. 

General property Natural property Achieved by mutation or by acquisition of plasmid or transposon (Tn)... 

Schenk S, A Hoelz, B Krauss, K Decker (1998) Gene structures and properties of enzymes of the plasmid-encoded nicotine catabolism of Arthrobacter nicotinovorans. J Mol Biol 284 1323-1339. 

Most of the known microorganisms to be active for BDS (by the date that patent [408] was introduced), were considered in this invention. Furthermore, their mutational or engineered derivatives, enzymes, cell-free extracts, recombinant enzymes, recombinant DNA, plasmids, vectors, and fragments were also incorporated in the intellectual property document. The mentioned operating conditions regard ambient temperature, mechanical agitation and a 1 9 biocatalyst/petroleum ratio. 

Many plasmids are known to possess three properties (1) increased resistance to the bactericidal effects of UV and chemical mutagens, (2) increased spontaneous mutagenesis, and (3) increased susceptibility to UV and chemically induced mutagenesis. Some plasmids possess all three properties others may possess just one, for example, increased susceptibility to mutagenesis (review Mortelmans and Dousman, 1986). Often the profile of activity depends on the DNA repair status of the host cell (Pinney, 1980). Plasmid pKMIOl carries DNA repair genes and has been widely used in strains used in bacterial mutagenicity tests. 

Mortelmanns, K.E. and Strocker, B.A.D. (1979). Segregation of the mutator property of plasmid R46 from its ultraviolet-protecting property. Mol. Gen. Genet. 167 317-328. 

Formation of a complex between DNA and polycationic compounds appears to be the initial and quite possibly a critical parameter for nonviral gene delivery. Several synthetic vector systems, which are generally cationic in nature, including poly(lysines), cationic liposomes or various types of block copolymers and recently dendrimers, have been shown to self-assemble with plasmid DNA [13-15] [16]. Specific physicochemical properties manifested by these DNA complexes depend on the type of cationic agent used however, interesting patterns for such interactions are beginning to evolve [17, 18]. Under certain conditions, the interaction of DNA with polyvalent cations results in... 

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