INDUCTION OF THE NAG REGULON OF ESCHERICHIA-COLI BY N-ACETYLGLUCOSAMINE AND GLUCOSAMINE - ROLE OF THE CYCLIC AMP-CATABOLITE ACTIVATOR PROTEIN COMPLEX IN EXPRESSION OF THE REGULON

The divergent nag regulon located at 15.5 min on the Escherichia coli map encodes genes necessay for growth on N-acetylglucosamine and glucosamine. Full induction of the regulon requires both the presence of N-acetylglucosamine and a functional cyclic AMP (cAMP)-catabolite activator protein (CAP) complex. Glucosamine produces a lower level of induction of the regulon. A nearly symmetric consensus CAP-binding site is located in the intergenic region between nagE (encoding EII(Nag)) and nagB (encoding glucosamine-6-phosphate deaminase). Expression of both nagE and nagB genes is stimulated by cAMP-CAP, but the effect is more pronounced for nagE. In fact, very little expression of nagE is observed in the absence of cAMP-CAP, whereas 50% maximum, expression of nagB is observed with N-acetylglucosamine in the absence of cAMP-CAP. Two mRNA 5' ends separated by about 100 nucleotides were located before nagB, and both seem to be similarly subject to N-acetylglucosmaine induction and cAMP-CAP stimulation. To induce the regulon, N-acetylglucosamine or glucosamine must enter the cell, but the particular transport mechanism used is not important.