Dramatic changes in Fis levels upon nutrient upshift in Escherichia coli

Abstract

Fis is a small basic DNA-binding protein from Escherichia coli that was identified because of its role in site-specific DNA recombination reactions. Recent evidence indicates that Fis also participates in essential cell processes such as rRNA and tRNA transcription and chromosomal DNA replication. In this report, we show that Fis levels vary dramatically during the course of cell growth and in response to changing environmental conditions. When stationary-phase cells are subcultured into a rich medium, Fis levels increase from less than 100 to over 50,000 copies per cell prior to the first cell division. As cells enter exponential growth, nascent synthesis is largely shut off, and intracellular Fis levels decrease as a function of cell division. Fis synthesis also transiently increases when exponentially growing cells are shifted to a richer medium. The magnitude of the peak of Fis synthesis appears to reflect the extent of the nutritional upshift. fis mRNA levels closely resemble the protein expression pattern, suggesting that regulation occurs largely at the transcriptional level. Two RNA polymerase-binding sites and at least six high-affinity Fis-binding sites are present in the fis promoter region. We show that expression of the fis operon is negatively regulated by Fis in vivo and that purified Fis can prevent stable complex formation by RNA polymerase at the fis promoter in vitro. However, autoregulation only partially accounts for the expression pattern of Fis. We suggest that the fluctuations in Fis levels may serve as an early signal of a nutritional upshift and may be important in the physiological roles Fis plays in the cell.

Modulation of the nucleoid, the transcription apparatus, and the translation machinery in bacteria for stationary phase survival

“…These nine proteins play regulatory roles in the replication of genome DNA and/ or the transcription of growth-related genes. For instance, Fis plays a role in transcription activation of genes highly expressed in growing cells (Ball et al 1992;Bokal et al 1995). FIS and RNA polymerase form a specific nucleoprotein complex at a stable RNA promoter (Muskhelishvili et al 1993).…”

FIS modulates growth phase‐dependent topological transitions of DNA in Escherichia coli

“…If we assume a 25 bp binding site for FIS (Pan et al, 1996), there would be 160 000-350 000 binding sites of varying affinity for FIS per 1 or 2.2 genome equivalents per E. coli cell. The calculated maximal number of FIS molecules in the cell is 50 000 dimers (Ball et al, 1992), which gives a FIS/DNAbinding site ratio of 0.31 and 0.14 for 1 and 2.2 genome equivalents respectively. The maximum abundance is similar to that of the other major nucleoid-associated proteins, HU, H-NS and IHF (Schmid, 1990).…”

“…Thus, it is reasonable to assume that the FIS-dependent alterations in the cellular levels of HU and H-NS proteins contribute to the observed differences in the supercoiling level between CSH50 and CSH50fis::kan cells. As there are only some hundred copies of FIS in stationary cells (Ball et al, 1992), it is conceivable that the induction of the intermediate subpopulation of topoisomers in stationary cells is mediated via the indirect effects of FIS on the cellular levels of HU, H-NS and perhaps IHF (Yasuzawa et al, 1992;Malik et al, 1996). In addition, we do not know at present whether FIS interacts directly with cellular topoisomerases to modulate their activity or perhaps affects the expression of top A and gyrA/gyr B promoters at the transcriptional level.…”

“…Furthermore, by maintaining the topological diversity of DNA in exponentially growing cells, FIS would increase the 'structural information' required for fine tuning of cellular processes involving DNA transactions. During the growth phase, the level of FIS drops, presumably because of the dilution of protein in the course of successive cellular divisions without degradation of the protein produced (Ball et al, 1992). It is conceivable that the sequential dissociation of FIS during the growth cycle from chromosomal sites with binding constants varying from micromolar to nanomolar range (Pan et al, 1996) could allow for correct timing of occupation by regulatory proteins of biologically important DNA loci, such as promoters, replication origins or recombination sequences (see for example Thompson et al, 1987;Cassler et al, 1995).…”

“…under conditions at which stationary cells are committed to start active growth (Kostrewa et al, 1991;Yuan et al, 1991;Ball et al, 1992;Ninnemann et al, 1992). At its maximum levels, FIS is present in 50 000-100 000 copies per cell (Ball et al, 1992), similar in abundance to the nucleoid-associated proteins HU, H-NS and IHF (Schmid, 1990). Recent studies reveal FIS as a general regulator of cellular metabolism (Xu and Johnson, 1995;Gonzá lez-Gil et al, 1996).…”