page_title: Fis
section_title: Properties and functions
hierarchical_section_title: Fis / Properties and functions
caption_attribution_description: English: dna negative supercoiling with fis
context_page_description: fis is an E. coli gene encoding the Fis protein. The regulation of this gene is more complex than most other genes in the E. coli genome, as Fis is an important protein which regulates expression of other genes. It is supposed that fis is regulated by H-NS, IHF and CRP. It also regulates its own expression. Fis is one of the most abundant DNA binding proteins in Escherichia coli under nutrient-rich growth conditions.
context_section_description: Fis is a very important small nucleotide-associated protein which plays a role in affecting the bacterial chromosome structure and the initiation of DNA replication. It is a nucleoid-associated protein in Escherichia coli that is abundant during early exponential growth in rich medium but is in short supply during stationary phase.  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. Expression of this fis operon is negatively regulated by Fis in vivo and 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. Fluctuations in Fis levels have been shown to serve as an early signal of a nutritional upshift and is important in the physiological roles Fis plays in the cell.
  It is a global regulatory protein in Escherichia coli that activates ribosomal RNA (rRNA) transcription by binding to three upstream activation sites of the rRNA promoter and enhances transcription 5 to 10 fold in vivo. Fis overexpression results in different effects on cell growth depending on nutrient conditions. The Fis nucleoid protein is differentiated by its fast increase in synthesis rates following nutrient upshifts and its abundance in rapidly growing E. coli cells.
  Fis has been known to activate ribosomal RNA transcription, as well other genes. It has a direct role in upstream activation of rRNA promoters. Fis binds to a recombinational enhancer sequence that is required to stimulate hin-mediated DNA inversion. It has also been shown to prevent initiation of DNA replication from oriC.
  It has been shown that sequences from 32 to 94 nucleotides upstream of the fis AUG are responsible for increasing fis lacZ translation reporter activities over 100 fold. Within this region, an AU sequence element centered 35 nucleotides upstream of the fis AUG increases fis translation by as much as 15 fold. Formation of a supposed RNA secondary structure element beginning 50 nucleotides upstream of the AUG also positively affects fis translation by up to 10 fold. The fis gene is cotranscribed with the upstream dusB gene encoding a tRNA-modifying enzyme. DusB protein levels are very low even under conditions when there is high transcription of the operon and high levels of Fis protein.
  Fis has been deemed a bacterial chromatin architectural protein.
  Besides modulating chromatin architecture, it is known to influence numerous promoters of E. coli and several other bacteria. Both in vivo and in vitro studies indicate that Fis acts as a transcriptional repressor of ''mom'' promoter. There is data that shows Fis mediates its repressive effect by denying access to RNA polymerase at the mom promoter. combined A repressive effect of Fis and previously characterized negative regulatory factors could be responsible to keep the gene silenced most of the time. In addition to bringing about overall downregulation of the Mu genome, it also ensures silencing of the advantageous but potentially lethal mom gene.
  Fis as a critical regulator of capsule expression. Fis is also involved in the regulation of a range of genes in bacterial species such as P. multocida, Enteroaggregative Escherichia coli, similar organisms. Some of these genes include important virulence factors.
caption: DNA negative supercoiling
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