Minipreparation of plasmid DNA is a rapid, small-scale isolation of plasmid DNA from bacteria. It is based on the alkaline lysis method invented by the researchers Birnboim and Doly in 1979. The extracted plasmid DNA resulting from performing a miniprep is itself often called a "miniprep".
When bacteria are lysed under alkaline conditions both DNA and proteins are precipitated. Some scientists reduce the concentration of NaOH used to 0.1M in order to reduce the occurrence of ssDNA.So therefore during denature of plasmid and supercoiled DNA added 5%sugar then denature slowly. After the addition of acetate-containing neutralization buffer the large and less supercoiled chromosomal DNA and proteins precipitate, but the small bacterial DNA plasmids can renature and stay in solution. Addition of phenol/chlorofrom can dissolve and denature proteins, like DNase. This is especially important if the plasmids are to be used for enzyme digestion. Otherwise, smearing may occur in enzyme restricted form of plasmid DNA.
Minipreps are used in the process of molecular cloning to analyze bacterial clones. A typical plasmid DNA yield of a miniprep is 20 to 30 µg depending on the cell strain.
Miniprep Protocols
http://www.protocol-online.org/prot/Molecular_Biology/Plasmid/Miniprep/
References
A rapid alkaline extraction procedure for screening recombinant plasmid DNA.
Birnboim HC, Doly J Nucleic Acids Res. 1979 Nov 24;7(6):1513-23.
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