PtrR (YneJ) is a novel E. coli transcription factor regulating the putrescine stress response and glutamate utilization

Although polyamines, such as putrescine (Ptr), induce envelope stress for bacteria, they are important as nitrogen and carbon sources. Ptr utilization in Escherichia coli involves protein glutamylation, and glutamate stands at a crossroads between catabolism and anabolism. This communication reports that the transcription factor YneJ, here renamed PtrR, is involved in the regulation of a small regulatory RNA gene, fnrS, and an operon, yneIHGF, encoding succinate-semialdehyde dehydrogenase, Sad (YneI), glutaminase, GlsB (YneH), and several other genes. The yneI promoter is activated during putrescine utilization under nitrogen/carbon starvation conditions, and we show that PtrR is important for the putrescine stress response. It is also a repressor of fnrS gene expression, involved in the cascade regulation of mRNA synthesis for the marA and sodB genes, involved in antibiotic responses. PtrR transcriptional regulation of fnrS leads to a regulatory cascade induced by this small RNA that affects mRNA levels of ompF and the multidrug resistance regulator, MarA. We propose that PtrR functions as a dual activator/repressor, and that its regulation is important for the responses to different stress conditions involving L-glutamine/L-glutamate and putrescine utilization.