Use of a modified Escherichia coli trpR gene to obtain tight regulation of high-copy-number expression vectors.

It has been found that with high-copy-number vectors utilising the Escherichia coli trp promoter the amount of repressor protein produced from the single chromosomally located trpR gene is inadequate for tight repression to be obtained. An attempt has been made to overcome this problem by inserting the trpR gene in cis into the expression vector. This proved unsuccessful because transcription from the trp promoter of such a plasmid could not be induced with 3,beta-indole acrylic acid, probably because the trpR gene is autogenously regulated. However, it was found that when the natural trpR promoter was replaced with a relatively weak constitutive promoter a useful self-repressible vector could be formed. A modified trpR gene of this type has been used to obtain tightly controlled expression of human interferon-beta (IFN-beta) from a vector having a copy number of 400. Tight regulation is particularly important in this case as IFN-beta is highly toxic to the E. coli cell.