Abstract

β-galactosidase activity of Escherichia coli cells containing operon fusion nhaA'-'lacZ was monitored to study the regulation of expression of nhaA gene under various conditions. The expression of the fusion was enhanced only by chemicals containing Na^+ or Li^+. This Na^+ or Li^+. This Na^+(Li^+)-specific enhancement of β-galactosidase activity represented the increase in the rate of synthesis of β-galactosidase rather than the decrease in the breakdown rate. The induction pattern was influenced by copy numbers of the gene. Induction by Na^+ or Li^+ was concentration and time dependent, reaching maximum 5-6 fold induction after 2 hours at 0.4-0.5 M for Na^+ or at 0.25-0.35 M for Li^+, Although the expression was induced at much lower concentration of Na^+ at alkaline pH values than at neutral pH in the presence of Na^+, alkaline pH itself did not induced the expression of the fusion in the absence of Na^+. Temperature shift and growth phase of culture did not affect the level of induction.

• Keywords: E. coli; Na^+; pH regulation; fusion