Katabolitrepression durch Nicht-PTS-Kohlenstoffquellen in Escherichia coli am Beispiel des Glycerineffekts

Abstract

The formation of glycerol-3-phosphate (G3P) in cells growing on tryptone broth causes catabolite repression as shown by the reduction of malT expression. For this repression to occure the general protein of the PEP-dependent phosphotransferase system (PTS), in particular EIIAGlc, as well as the adenylate cyclase and the cAMP/CRP system have to be present. In contrast to the effect of glucose that causes a dramatic shift of the EIIAGlc level to the dephosphorylated form, G3P only slightly increases the amount of dephosphorylated EIIAGlc. A mutant carrying a C-terminal deletion in adenylate cyclase was no longer subject to G3P-mediated catabolite repression. The conclusion of this is that the stimulation of adenylate cyclase by phosphorylated EIIAGlc is controlled by G3P, as well as by other sugar phosphates like glucose-6-phosphate. Further metabolism of these compounds is not necessary for repression.There is also a translational repression which is independent of cAMP/CRP and EIIAGlc, but pH-mediated. The effect does not occure in buffered media and in some strains with mutations affecting metabolism and growth rate.The pleiotropic nature of G3P-mediated repression was shown by the method of two-dimensional gel electrophoresis. Among the proteins repressed by glycerol are periplasmic binding proteins, enzymes of tricarbonic acid cycle, aldehyde dehydrogenase, Dps (a stress-induced DNA binding protein) and D-tagatose-1,6-bisphosphate aldolase.