AUTHOR=Brandi Anna , Giangrossi Mara , Giuliodori Anna M. , Falconi Maurizio 

TITLE=An Interplay among FIS, H-NS, and Guanosine Tetraphosphate Modulates Transcription of the Escherichia coli cspA Gene under Physiological Growth Conditions

JOURNAL=Frontiers in Molecular Biosciences

VOLUME=3

YEAR=2016

URL=https://www.frontiersin.org/journals/molecular-biosciences/articles/10.3389/fmolb.2016.00019

DOI=10.3389/fmolb.2016.00019

ISSN=2296-889X

ABSTRACT=<p>CspA, the most characterized member of the <italic>csp</italic> gene family of <italic>Escherichia coli</italic>, is highly expressed not only in response to cold stress, but also during the early phase of growth at 37°C. Here, we investigate at molecular level the antagonistic role played by the nucleoid proteins FIS and H-NS in the regulation of <italic>cspA</italic> expression under non-stress conditions. By means of both probing experiments and immunological detection, we demonstrate <italic>in vitro</italic> the existence of binding sites for these proteins on the <italic>cspA</italic> regulatory region, in which FIS and H-NS bind simultaneously to form composite DNA-protein complexes. While the <italic>in vitro</italic> promoter activity of <italic>cspA</italic> is stimulated by FIS and repressed by H-NS, a compensatory effect is observed when both proteins are added in the transcription assay. Consistently with these findings, inactivation of <italic>fis</italic> and <italic>hns</italic> genes reversely affect the <italic>in vivo</italic> amount of <italic>cspA</italic> mRNA. In addition, by means of strains expressing a high level of the alarmone guanosine tetraphosphate ((p)ppGpp) and <italic>in vitro</italic> transcription assays, we show that the <italic>cspA</italic> promoter is sensitive to (p)ppGpp inhibition. The (p)ppGpp-mediated expression of <italic>fis</italic> and <italic>hns</italic> genes is also analyzed, thus clarifying some aspects of the regulatory loop governing <italic>cspA</italic> transcription.</p>