Post-translational and transcriptional regulation of polyamine biosynthesis in Escherichia coli

Ornithine and arginine decarboxylases (ODC and ADC) of Escherichia coli are inhibited post-translationally by antizyme and ribosomal proteins S20 and L34. The inhibition of either enzyme is relieved when excess of the other decarboxylase is added. Using this approach, in vitro as well as in vivo, we demonstrate that the extent of the post-translational inhibition of ODC and ADC in E. coli is at least 65 and 50%, respectively. The inhibited enzyme levels increase even further upon exposure of cells to polyamines. The post-translational mode of regulation can counteract a 4-fold increase of ODC protein in the cell. The negative transcriptional regulation of ODC and ADC expression by polyamines is mediated by transcription factors and not by direct polyamine effects on the promoters of their genes. Three proteins interacting with the ODC promoter region were found by southwestern blot analysis.