Construction of a Plasmid for High Level Expression of XMP Aminase in Escherichia coli

Abstract

In order to produce 5'-guanylic acid (GMP) from 5'-xanthylic acid (XMP), we attempted to increase the activity of the conversion enzyme, XMP aminase (EC 6.3.4.1), in Escherichia coli. We subcloned the guaA gene coding for XMP aminase from plasmid pLC34-10 into pBR322. By connecting the tryptophan (trp) promoter at a suitable position upstream of the guaA gene, we obtained plasmid pXAR33. E. coli K294/pXAR33 showed an increase in activity of approximately 80 times when compared with K294, and the amount of the enzyme protein represented approx. 10% of the total cellular protein. The production of GMP with the plasmid carrying strain was also investigated.