Accumulation of glucose 6-phosphate or fructose 6-phosphate is responsible for destabilization of glucose transporter mRNA in Escherichia coli

Previously we found that a mutation in either pgi or pfkA, encoding phosphoglucose isomerase or phosphofructokinase X respectively, facilitates degradation of the ptsG mRNA in an RNase E-dependent manner in Escherichia coli (1). In this study, we examined the effects of a series of glycolytic genes on the degradation of ptsG mRNA and how the mutations destabilize the ptsG mRNA. The conditional lethal mutation ts8 in fda, encoding fructose-1,6-P-2 aldolase just downstream of pthA in the glycolytic pathway, caused the destabilization of ptsG mRNA at the nonpermissive temperature. Mutations in any other gene did not destabilize the ptsG mRNA, rather, they reduced the ptsG transcription mainly by affecting the cAMP level. The rapid degradation of ptsG mRNA in mutant strains was completely dependent upon the presence of glucose or any one of its compounds, which enter the Embden-Meyerhof glycolytic pathway before the block points. A significant increase in the intracellular glucose-6-P level was observed in the presence of glucose in the pgi strain. An overexpression of glucose-6-phosphate dehydrogenase eliminated both the accumulation and the degradation of ptsG mRNA in the pgi strain. In addition, accumulation of fructose-6-P led to the rapid degradation of ptsG mRNA in a pgi,pfkA mutant strain lacking glucose-6-P. We conclude that the RNase E-dependent destabilization of ptsG mRNA occurs in response to accumulation of glucose-6-P or fructose-6-P.