A VERSATILE PLASMID VECTOR SYSTEM FOR THE REGULATED EXPRESSION OF GENES IN ESCHERICHIA-COLI

A series of plasmid expression vectors, which support the regulated an d efficient expression of genes in Escherichia coli, have been constru cted. The vectors consist of a DNA replication origin cassette, a prom oter cassette, an efficient ribosome binding site together with a poly linker region and a lacZ gene. Several types of replication origins an d promoter sequences are each available on cassettes. Fusion of the 5' TG dinucleotide of the gene under consideration to the A nucleotide, present on the vector, results in an ATG start codon and allows, in co mbination with the plasmid-borne ribosome binding site, the efficient expression of the cloned gene. Additionally, a second fusion of the ge ne at its 3' end with the lacZ gene, which is available in all three r eading frames relative to the polylinker region, allows rapid selectio n of the correctly fused genes. As an example of the cloning of a regu latory gene, this vector system was used for the expression of the dna A gene, of Escherichia coli, the initiator protein for DNA replication .