Common and divergent features in transcriptional control of the homologous small RNAs GlmY and GlmZ in Enterobacteriaceae

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Abstract
Small RNAs GlmY and GlmZ compose a cascade that feedback-regulates synthesis of enzyme GlmS in Enterobacteriaceae. Here, we analyzed the transcriptional regulation of glmY/glmZ from Yersinia pseudotuberculosis, Salmonella typhimurium and Escherichia coli, as representatives for other enterobacterial species, which exhibit similar promoter architectures. The GlmY and GlmZ sRNAs of Y. pseudotuberculosis are transcribed from σ54-promoters that require activation by the response regulator GlrR through binding to three conserved sites located upstream of the promoters. This also applies to glmY/glmZ of S. typhimurium and glmY of E. coli, but as a difference additional σ70-promoters overlap the σ54-promoters and initiate transcription at the same site. In contrast, E. coli glmZ is transcribed from a single σ70-promoter. Thus, transcription of glmY and glmZ is controlled by σ54 and the two-component system GlrR/GlrK (QseF/QseE) in Y. pseudotuberculosis and presumably in many other Enterobacteria. However, in a subset of species such as E. coli this relationship is partially lost in favor of σ70-dependent transcription. In addition, we show that activity of the σ54-promoter of E. coli glmY requires binding of the integration host factor to sites upstream of the promoter. Finally, evidence is provided that phosphorylation of GlrR increases its activity and thereby sRNA expression.