Abstract
The nucleoid-associated protein FIS is a global regulator of gene expression and chromosome structure in Escherichia coli and Salmonella enterica. Despite the importance of FIS for infection and intracellular invasion, very little is known about the regulation of S. enterica fis expression. Under standard laboratory growth conditions, fis is highly expressed during rapid growth but is then silenced as growth slows. However, if cells are cultured in non-aerated conditions, fis expression is sustained during stationary phase. This led us to test whether the redox-sensing transcription factors ArcA and FNR regulate S. enterica fis. Deletion of FNR had no detectable effect, whereas deletion of ArcA had the unexpected effect of further elevating fis expression in stationary phase. ArcA required RpoS for induction of fis expression, suggesting that ArcA indirectly affects fis expression. Other putative regulators were found to play diverse roles: FIS acted directly as an auto-repressor (as expected), whereas CRP had little direct effect on fis expression. Deleting regions of the fis promoter led to the discovery of a novel anaerobically-induced transcription start site (Pfis-2) upstream of the primary transcription start site (Pfis-1). Promoter truncation also revealed that the shortest functional fis promoter was incapable of sustained expression. Moreover, fis expression was observed to correlate directly with DNA supercoiling in non-aerated conditions. Thus, the full-length S. enterica fis promoter region may act as a topological switch that is sensitive to stress-induced duplex destabilisation and up-regulates expression in non-aerated conditions.
Highlights
The factor for inversion stimulation (FIS) is a global regulator of gene expression and chromosome compaction in Gammaproteobacteria
FIS is a global regulator of gene expression, but its abundance in the cell fluctuates dramatically depending on growth phase
During periods of rapid growth in laboratory conditions the fis promoter is highly expressed, which accounts for the high levels of FIS protein during exponential growth
Summary
The factor for inversion stimulation (FIS) is a global regulator of gene expression and chromosome compaction in Gammaproteobacteria. Control of fis expression is best understood in E. coli, where the global regulatory proteins CRP, IHF, and FIS modulate only the degree of induction, but none of them is absolutely required for fis expression in laboratory culture [4,5,6]. In their absence, fis continues to be induced by nutritional upshift and repressed during stationary phase [4,5,6]. Stringently-regulated promoters respond negatively to the alarmone guanosine tetraphosphate (ppGpp) and to the protein DksA, both of which act via RNA polymerase [10,11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
