Kai Mikael Korpela

Determination of plasmid copy number with nucleic acid sandwich hybridization

Abstract Sandwich hybridization is a convenient method for the detection and quantification of specific genes. Here we have used the sandwich hybridization method for determining the copy number of cloning vectors. The Saccharomyces cerevisiae expression vector pAAH5 was present in 10 copies per yeast cell. Derivatives of the Escherichia coli plasmid pBR322 had copy numbers of around 15 increasing to 250 upon amplification with chloramphenicol as detected per genome equivalent. The mutant pHCl, derived from pBR322, was found in up to 2500 copies per bacterial chromosome in an unamplified culture.