Some important bacterial genes are not located in the main chromosomal DNA but in independently replicating molecules of circular, double-stranded, ‘plasmid’ DNA. Such genes include those for antibiotic resistance, antibiotic synthesis, toxin production, nitrogen fixation, production of degradative enzymes, and conjugation; so plasmids are obviously of interest in their own right. However, in the context of this book, plasmids are mainly of interest as ‘vectors’ for the cloning of DNA molecules. As will be seen in chapters 11 and 12, it is possible to obtain large quantities of a particular DNA (e.g. cDNA — see Chapter 9) by inserting it into plasmid DNA, to give enlarged plasmids (‘vector’ plasmids) which can be introduced into a suitable host bacterium in which they will replicate. Culture of the cells will result in the production of more plasmid DNA, which can then be isolated from the cells and the inserted DNA recovered.
KeywordsBuoyant Density Plasmid Isolation Vertical Rotor Preparative Electrophoresis Nucleic Acid Preparation
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