Low-copy-number plasmid-cloning vectors amplifiable by derepression of an inserted foreign promoter

Tandem promoters determine regulation of the Klebsiella pneumoniae glutamine synthetase (glnA) gene

Transcription of the structural gene for glutamine synthetase (glnA) in Klebsiella pneumoniae is controlled by the nitrogen regulatory genes ntrA, ntrB and ntrC. The nucleotide sequence of the regulatory region upstream of the glnA gene is reported here. High resolution S1 mapping of in vivo transcripts indicates that the regulatory region contains tandem promoters separated by 100 nucleotides. Measurements of beta-galactosidase activities determined in vivo from glnA-lac fusions suggest that the upstream promoter (for RNA2) is negatively regulated by the ntrBC gene products whereas transcription from the downstream promoter (for RNA1) is positively activated by the ntrA gene product in the presence of either the ntrBC or the nifA genes. The nucleotide sequence of the upstream promoter resembles the consensus sequence for E. coli promoters, whereas the downstream promoter shows homology with the nitrogen fixation (nif) promoters of K. pneumoniae.

Dual-origin plasmid vectors whose origin of replication is controlled by the coliphage lambda promoter pL

The insertion of an XhoI linker 30 bp from the 5' end of the RNA II primer for ColE1 plasmid replication has allowed us to replace the natural RNA II promoter by other controllable promoters, in particular lambda pL. Manipulation of this modified origin was facilitated by constructing dual-origin plasmids, stable maintenance being directed by the pSC101 origin. Experiments showed that such dual-origin plasmids could be stably maintained at approximately four copies per chromosome at 30 degrees C and readily amplified by thermal induction of strains carrying a thermolabile lambda repressor. The use of such plasmids for the construction of stable, amplifiable expression vectors is discussed.