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Journal of Bacteriology, January 1999, p. 197-203, Vol. 181, No. 1
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Protein Mobility in the Cytoplasm of Escherichia coli

Michael B. Elowitz,1,2,* Michael G. Surette,2,dagger Pierre-Etienne Wolf,1,2,Dagger Jeffry B. Stock,2 and Stanislas Leibler1,2

Departments of Physics1 and Molecular Biology,2 Princeton University, Princeton, New Jersey 08544

Received 7 August 1998/Accepted 21 October 1998

The rate of protein diffusion in bacterial cytoplasm may constrain a variety of cellular functions and limit the rates of many biochemical reactions in vivo. In this paper, we report noninvasive measurements of the apparent diffusion coefficient of green fluorescent protein (GFP) in the cytoplasm of Escherichia coli. These measurements were made in two ways: by photobleaching of GFP fluorescence and by photoactivation of a red-emitting fluorescent state of GFP (M. B. Elowitz, M. G. Surette, P. E. Wolf, J. Stock, and S. Leibler, Curr. Biol. 7:809-812, 1997). The apparent diffusion coefficient, Da, of GFP in E. coli DH5alpha was found to be 7.7 ± 2.5 µm2/s. A 72-kDa fusion protein composed of GFP and a cytoplasmically localized maltose binding protein domain moves more slowly, with Da of 2.5 ± 0.6 µm2/s. In addition, GFP mobility can depend strongly on at least two factors: first, Da is reduced to 3.6 ± 0.7 µm2/s at high levels of GFP expression; second, the addition to GFP of a small tag consisting of six histidine residues reduces Da to 4.0 ± 2.0 µm2/s. Thus, a single effective cytoplasmic viscosity cannot explain all values of Da reported here. These measurements have implications for the understanding of intracellular biochemical networks.

* Corresponding author. Mailing address: Lewis Thomas Lab, Washington Rd., Princeton, NJ 08544. Phone: (609) 258-1574. Fax: (609) 258-6175. E-mail: melowitz{at}princeton.edu.

dagger Present address: Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alberta, Canada T2N 4N1.

Dagger Present address: Centre de Recherches sur les Très Basses Températures, CNRS, Laboratoire associé à l'Université Joseph Fourier, F-38042 Grenoble Cedex 9, France.

Journal of Bacteriology, January 1999, p. 197-203, Vol. 181, No. 1
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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