Plasmid pKKH : an improved vector with higher copy number for expression of foreign genes in Escherichia coli

An improved vector of 2889 bp was constructed by mutation of copy number control system, into which foreign genes without or with the start codon ATG can be directly inserted for high-level expression in Escherichia coli deletion of the rop gene encoding a negative regulation protein ROP leads to increase the plasmid copy number, and finally makes the vector increase expression level more than 60% in comparison with initial one.