PLoS ONE (Jan 2012)

The CnuK9E H-NS complex antagonizes DNA binding of DicA and leads to temperature-dependent filamentous growth in E. coli.

  • Sang Hoon Yun,
  • Sang Chun Ji,
  • Heung Jin Jeon,
  • Xun Wang,
  • Si Wouk Kim,
  • Geunu Bak,
  • Younghoon Lee,
  • Heon M Lim

DOI
https://doi.org/10.1371/journal.pone.0045236
Journal volume & issue
Vol. 7, no. 9
p. e45236

Abstract

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Cnu (an OriC-binding nucleoid protein) associates with H-NS. A variant of Cnu was identified as a key factor for filamentous growth of a wild-type Escherichia coli strain at 37°C. This variant (CnuK9E) bears a substitution of a lysine to glutamic acid, causing a charge reversal in the first helix. The temperature-dependent filamentous growth of E. coli bearing CnuK9E could be reversed by either lowering the temperature to 25°C or lowering the CnuK9E concentration in the cell. Gene expression analysis suggested that downregulation of dicA by CnuK9E causes a burst of dicB transcription, which, in turn, elicits filamentous growth. In vivo assays indicated that DicA transcriptionally activates its own gene, by binding to its operator in a temperature-dependent manner. The antagonizing effect of CnuK9E with H-NS on DNA-binding activity of DicA was stronger at 37°C, presumably due to the lower operator binding of DicA at 37°C. These data suggest that the temperature-dependent negative effect of CnuK9E on DicA binding plays a major role in filamentous growth. The C-terminus of DicA shows significant amino acid sequence similarity to the DNA-binding domains of RovA and SlyA, regulators of pathogenic genes in Yersinia and Salmonella, respectively, which also show better DNA-binding activity at 25°C.