Enterococcus hirae vacuolar ATPase is expressed in response to pH as well as sodium

The Enterococcus hirae ntp operon encodes both a vacuolar ATPase, which tra nsports Na+ as well as Li+, and the KtrII K+ transporter. A plasmid, in whi ch the chloramphenicol acetyltransferase gene (CAT) was placed downstream o f the ntp promoter, was introduced into a mutant totally defective in Na+ e xtrusion, The CAT activity of this transformant was increased preferentiall y by addition of NaCl, but not by LiCl, in the media or by elevating the me dium pH, correlating well with the increase in amounts of the ATPase subuni ts observed by Western blotting. The physiological significance of these re sponses of the ntp promoter is discussed, (C) 1999 Federation of European B iochemical Societies.