Background

One of the most fascinating processes in a living cell, the cell division cycle, is tightly coordinated in space and time. In the case of bacteria, the relative simplicity of internal organization leads us to believe that this complicated biological process can be deconvolved into a series of physical interactions driving chemical kinetic steps. It has recently become evident that specific DNA- and protein-membrane interactions are essential in the main bacterial cell cycle events - initiation of DNA replication, chromosome segregation and constriction/septation, leading to division. Membrane domains created around rapidly replicating and transcribed DNA were proposed to serve in both temporal and spatial control of the cell cycle propagation. We consider membrane heterogeneity as the principal control in the regulation of the bacterial cell cycle.

Current Projects

1. To gain insight into the distribution and dynamics of membrane domains in bacteria and their relation to DNA replication and cell division. We investigate a new mechanism for the formation of membrane domains based on coupled transcription/translation/insertion (transertion). Measuring membrane dynamics and domain formation by exploiting different fluorescent membrane probes, fluorescence spectroscopy, fluorescence microscopy imaging and single-molecule techniques.

2. Establish the role of membrane domains in the membrane targeting, assembly, and function of the key cell cycle proteins. Membrane domains of specific composition were proposed to serve in the regulation of activity and assembly of the key proteins at the right time and site. The advantage of this mechanism is that it provides a spatially localized signal for randomly distributed cytoplasmic proteins, like DnaA, FtsZ and MinCD, participating in temporal and spatial regulation mechanisms. DnaA and MinD belong to a growing set of proteins classified as amphitropic, which share the same property of reversible binding to membrane lipids. This process regulates their function and the binding affinity is subject to regulation both by adenine nucleotides and membrane composition. We study the molecular and biophysical nature of MinD- and DnaA-membrane interaction using fluorescence-spectroscopy methods.

3. Establish the role of nucleoid-membrane interaction and membrane domains in determination of nucleoid morphology. In Escherichia coli, two opposing forces are proposed to determine nucleoid morphology - compaction and expansion, originating from DNA negative supercoiling and DNA-membrane anchoring, respectively. We examine the existence of mechanical interaction between nucleoid and membrane, mediated by the transertion process.

4. Internal dynamics of isolated E. coli nucleoids. The topology and dynamics of DNA in a bacterial nucleoid affects the kinetics of such major processes as DNA replication, gene expression, morphology maintenance and chromosome segregation. We apply the Fluorescence Correlation Spectroscopy (FCS) technique to assess the internal dynamics of isolated E. coli nucleoids randomly labeled with the TOTO fluorophore. FCS measurement reveals that mobility, density and cooperativity in dynamics of DNA segments are sensitive to the degree of DNA supercoiling.

Recent Publications

Piro, O., Carmon, G., Feingold M. & I. Fishov (2013) 3D structure of the Z-ring as a random network of FtsZ filaments. Environmental Microbiology, doi: 10.1111/1462-2920.12197.

Fishov, I. & V. Norris (2012) Membrane heterogeneity created by transertion is a global regulator in bacteria. Curr Opin Microbiol 15: 724-730.

Regev, T., N. Myers, R. Zarivach & I. Fishov, (2012) Association of the chromosome replication initiator DnaA with the Escherichia coli inner membrane in vivo: quantity and mode of binding. PLoS One 7: e36441.

Tsukanov, R., G. Reshes, G. Carmon, E. Fischer-Friedrich, N. S. Gov, I. Fishov & M. Feingold, (2011) Timing of Z-ring localization in Escherichia coli. Phys Biol 8: 066003.

Mazor S, Regev T, Mileykovskaya E, Margolin W, Dowhan W, Fishov I. (2008) Mutual effects of MinD-membrane interaction: I. Changes in the membrane properties induced by MinD binding. Biochim Biophys Acta. 1778: 2496–2504. II. Domain structure of the membrane enhances MinD binding. Biochim Biophys Acta. 1778: 2505–2511.

Reshes G, Vanounou S, Fishov I, Feingold M. (2008) Timing the start of division in E. coli: a single-cell study. Phys Biol. 5(4):46001.

Ph.D. Institute of Biological Physics, Acad. of Sci. of USSR, 1983