GLUCOSE KINASE-DEPENDENT CATABOLITE REPRESSION IN STAPHYLOCOCCUS-XYLOSUS

By transposon Tn917 mutagenesis, 16 mutants of Staphylococcus xylosus were isolated that showed higher levels of beta-galactosidase activity in the presence of glucose than the wild-type strain. The transposons were found to reside in three adjacent locations in the genome of S. xylosus. The nucleotide sequence of the chromosomal fragment affected by the Tn917 insertions yielded an open reading frame encoding a prote in with a size of 328 amino acids with a high level of similarity to g lucose kinase from Streptomyces coelicolor, Weaker similarity was also found to bacterial fructokinases and xylose repressors of gram-positi ve bacteria, The gene was designated glkA. Immediately downstream of g lkA, two open reading frames were present whose deduced gene products showed no obvious similarity to known proteins, Measurements of catabo lic enzyme activities in the mutant strains grown in the presence or a bsence of sugars established the pleiotropic nature of the mutations. Besides beta-galactosidase activity, which had been used to detect the mutants, six other tested enzymes were partially relieved from repres sion by glucose. Reduction of fructose-mediated catabolite repression was observed for some of the enzyme activities. Glucose transport and ATP-dependent phosphorylation of HPr, the phosphocarrier of the phosph oenolpqruvate:carbohydrate phosphotransferase system involved in catab olite repression in gram-positive bacteria, were not affected. The clo ned glkA gene fully restored catabolite repression in the mutant strai ns in trans, Loss of GlkA function is thus responsible for the partial relief from catabolite repression. Glucose kinase activity in the mut ants reached about 75% of the wild-type level, indicating the presence of another enzyme in S. xylosus. However, the cloned gene complemente d an Escherichia coli strain deficient in glucose kinase. Therefore, t he glkA gene encodes a glucose kinase that participates in catabolite repression in S. xylosus.