A mutation which affects both the specificity of PtsG sugar transport and the regulation of ptsG expression by Mlc in Escherichia coli.

Normally glucosamine (GlcN) is not a substrate for EIICB(Glc) of the glucose phosphotransferase system (PTS), encoded by ptsG, but it is transported by the mannose (Man) PTS, encoded by manXYZ. A mutation, umgC, has been described in Escherichia coli which allows a strain mutated in the Man PTS to grow on GlcN. The umgC mutation was mapped to the ptsG region and was proposed to make ptsG expression constitutive. Transcription of ptsG is regulated by the repressor Mlc so that mutations in mlc enhance the expression of ptsG. An mlc mutation, however, is not sufficient to allow good growth on GlcN, unlike the umgC mutation. The umgC mutation is shown to enhance expression of ptsG even in the absence of any PTS sugar transport, but the increase is greater in the presence of GlcN or Man. The umgC mutation also increases expression of the ptsHI and manXYZ operons, which are both regulated by Mlc. The umgC mutation was sequenced and two mutations were found: one, G176D, within the IIC membrane domain and the second, E472K, within the soluble IIB domain of PtsG. The cloned UmgC allele shows the enhanced transport and regulatory characteristics of the chromosomal mutation. Analysis of the two mutations present individually on plasmids shows that the IIC mutation is responsible for both the effect on sugar specificity and regulation.