Cloning of the galactokinase gene (galK) from Streptomyces coelicolor A3(2)

Streptomyces coelicolor A3(2) and Streptomyces lividans 66 strains were shown to be sensitive to the galactose analogue 2-deoxy-D-galactose. Spontaneous resistant mutants were isolated that were Gal- and lacked the enzyme galactokinase. The galK gene (structural gene for galactokinase) from S. coelicolor was cloned into S. lividans using the low copy number vector pIJ922. The resulting plasmid (pMT650), which contained a 14 kb insert, complemented gal mutations in both species. The presence of the galK gene on a 2.8 kb EcoRI fragment was confirmed by expressing it in Escherichia coli where it complemented a well characterized galK mutation.