INTRACELLULAR NA-TYPE NA+ TRANSLOCATING ATPASE IN ENTEROCOCCUS-HIRAE(REGULATES TRANSCRIPTION OF THE NTP OPERON ENCODING A VACUOLAR)

The Gram-positive bacterium Enterococcus hirae has a vacuolar-type Na-translocating ATPase that is encoded by the ntp operon (ntpFIKECGABDH J) (Takase, K., Kakinuma, S., Yamato, I., Konishi, K., Igarashi, K., a nd Kakinuma, Y. (1994) J, Biol, Chem, 269, 11037-11044). Primer extens ion experiments identified the start site of transcription of this ope ron upstream of the ntpF gene, In parallel with the increases of both Na+-pumping activity in whole cells and Na+-stimulated ATPase activity in the membranes, the amounts of the two major subunits (A and B) of this enzyme increased remarkably in cells grown on medium containing h igh concentrations of NaCl but not on medium containing KCl or sorbito l, Chloramphenicol completely abolished the increases of the enzyme ac tivity and the amounts of A and B subunits, suggesting that the Na+-AT Pase level increased by de novo synthesis of the enzyme with the stimu lation of high concentrations of the external sodium ions. Finally, We stern blot and Northern blot experiments revealed that the increase in the Na+-ATPase level with the external Na+ was further accelerated by addition of an ionophore, such as monensin, which rendered the cell m embrane permeable to Na+. These results suggest that the transcription of the Na+-ATPase operon is regulated by the intracellular concentrat ion of sodium ions.