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  1. Factor for Inversion Stimulation
  2. Nucleoid-associated Protein
  3. Exponential growth phase at maximum, decreases to undetectable levels stationary phase
  4. Binds every 200-300 bases of DNA on average
  5. Highly expressed FIS does negative feedback

Fis is a small basic DNA-binding protein that was identified in E. coli as a factor involved in site-specific DNA recombination. Several lines of evidence indicate that Fis also participates in other processes of DNA functions such as transcription of the growth-related genes and DNA replication. The intracellular level of Fis protein in exponential growth phase cells of E. coli W3110 was found to be about 60,000 molecules per cell at maximum, but thereafter it decreased to undetectable levels in the stationary phase. Fis is the most abundant nucleoid-associated protein in growing E. coli cells. The growth-dependent change in the Fis level is in good agreement with the observations that Fis is needed for transcription of growth-related genes, such as those for rRNA and tRNA, and for DNA replication.

Our measurement of the intracellular Fis level agrees well with the observations that the Fis level in E. coli MC1000 growing under various conditions fluctuates within a range of less than 100 in the stationary phase to over 50,000 molecules per cell in the early-exponential growth phase. The regulation of fis is essentially the same in Salmonella typhimurium, even though the autoregulation is less efficient. The timing of the Fis peak occurs prior to the first cell division of cell growth after recovery from the stationary phase. If the DNA-bound Fis remains a homodimer, Fis may bind every 200 to 300 bp of DNA, on average, along the genome DNA in growing cells of E. coli (but the Fis sites are not regularly distributed along the genome DNA). Highly expressed Fis represses its own synthesis by binding to the fis promoter region. Upon entry into the stationary phase, Fis synthesis is switched off, resulting in a decrease in intracellular level by 500- to 1,000 fold.

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