CLONING AND CHARACTERIZATION OF THE GSK GENE ENCODING GUANOSINE KINASE OF ESCHERICHIA-COLI

The Escherichia coli gsk gene encoding guanosine kinase was cloned fro m the Kohara gene library by complementation of the E. coli gsk-1 muta nt allele. The cloned DNA fragment was sequenced and shown to encode a putative polypeptide of 433 amino acids with a molecular mass of 48,1 13 Da. Minicell analysis established the subunit M(r) as 43,500. Prime r extension analysis indicated the presence of an adequate Pribnow box and suggested that the transcript contained a 110-base leader sequenc e. Strains harboring the gsk gene on multicopy plasmids overexpressed both guanosine and inosine kinase activities. N-terminal sequence and amino acid composition analyses of the 43,500-M(r) polypeptide band co nfirmed the correct reading frame assignment and the identity of this band as the gsk gene product. Comparison of the amino acid sequence wi th the protein database revealed similarity to regions of other mononu cleotide utilizing enzymes.