EXPRESSION OF AN INDUCIBLE ENZYME-II FRUCTOSE AND ACTIVATION OF A CRYPTIC ENZYME-II GLUCOSE IN GLUCOSE-GROWN CELLS OF SPONTANEOUS MUTANTS OF STREPTOCOCCUS-SALIVARIUS LACKING THE LOW-MOLECULAR-MASS FORM OF IIIMAN, A COMPONENT OF THE PHOSPHOENOLPYRUVATE - MANNOSE PHOSPHOTRANSFERASE SYSTEM

We have reported previously that the phosphoenolpyruvate: mannose phosphotransferase system (mannose PTS) of Streptococcus salivarius, consisting of an Enzyme II mannose (EII(man)) and two forms of Enzyme III mannose (III(man)) With M(r) values of 38900 and 35200, respectively, concomitantly transports and phosphorylates mannose, as well as glucose and fructose. In this paper, we report the presence, in S. salivarius, of alternative specific fructose and glucose PTSs encoded by inducible and cryptic genes, respectively. Protein phosphorylation experiments conducted with [P-32]phosphoenolpyruvate have allowed us to identify by SDS-PAGE and autoradiography the EII fructose (EII(fru)) (M(r)57500) and the EII glucose (EII(glc)) (M(r)58700). No proteins corresponding to III(fru) or III(glc) could be detected. EII(fru) phosphorylated fructose on the C-1 position rather than, as with the constitutive mannose PTS, on the C-6 position. Growth on fructose resulted in the induction of EII(fru) as well as an increase of 1-phosphofructokinase activity. Nevertheless, the genes encoding these proteins were independently regulated. Studies carried out with spontaneous mutants lacking the low-molecular-mass form of III(man) (mutants A37, G29 and B31) showed that EII(fru) was expressed in glucose-grown cells of strains G29 and B31, but not in strain A37, whereas the cryptic gene encoding EII(glc) was activated in all three mutant strains. The results obtained with the mutants suggest that the three spontaneous mutants were not all mutated on the gene encoding III(man) although all of them lacked III(man).