Construction of Multicopy Expression Vectors for Regulated Over-production of Proteins in Klebsiella pneumoniae and Other Enteric Bacteria

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Abstract
A number of expression vectors have been constructed to allow over-production of selected gene products in Klebsiella pneumoniae and other enteric bacteria. The plasmids use the strong hybrid trp-lac (tac) promoter for gene expression, which is regulated by the lacIQ allele of the lac repressor carried on the vector. This provides very tight regulation of gene expression, which is important for over-production of proteins which may be detrimental to cell growth. The vectors carry the standard mp18 cloning nest in which all the restriction sites are unique to the plasmid (with the exception of EcoRI in pDK7). Derivatives were constructed carrying kanamycin, chloramphenicol or ampillicin resistance as selectable markers, the first two of which are advantageous in K. pneumoniae due to the high inherent .beta.-lactamase activity of this organism.