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Title: Noise in gene expression systems with monomer and dimer autoregulation
P151
Shibata, Tatsuo; Mikhailov, Alexander S.

shibata@fhi-berlin.mpg.de
Department of Physical Chemistry, Fritz-Harber-Institut der Max-Planck-Gesellshaft, Faradayweg 4-6, 14195 Berlin Germany.

The cell is a small system. Although the number of chemical species in a cell is quite large, the number of molecules of each type is often small. For instance, the number of mRNA molecules of a given type is typically fewer than ten copies per a cell. Under these conditions, strong fluctuations in the number of molecules must be present. For some systems, large fluctuations in the numbers of a protein are dangerous. The cellular systems should have reliability in order to properly respond to external stimuli. How does a cell achieve such reliability despite large fluctuations? The cell systems should possess some mechanisms that would allow them to reduce molecular noise.

Recently, time-resolved experimental measurements of gene expression have been performed. Noise in genetic networks has attracted much attention and fluctuations have been measured for a particular gene expression system [1, 2]. Moreover, time evolution of the activity of an individual gene in a larger genetic network has been recorded [3]. A challenging theoretical question is how the noise can be suppressed or enhanced in a genetic network.

In our theoretical study, fluctuations in the number of protein molecules in three simple gene expression systems are investigated. We first show that the noise in the elementary gene expression systems is larger than Poissonian [4]. A simple negative autoregulation may reduce the intensity of noise, but it also affects the mean number of proteins. In biological systems, negative autoregulation of genetic expression is often realized by multimers. We show that further noise reduction can be achieved by employing dimers for negative autoregulation. We discuss the way of how the dimerization process reduces the noise in the system [5].
[1] A. Becskei and L. Serrano, Nature 405 (2000) 590.
[2] A. van Oudenaarden et. al., Nature Genetics 31 (2002) 69.
[3] U. Alon, et. al., Science 292 (2001) 2080.
[4] M.Thattai and A. van Oudenaarden, Proc. Natl. Acad. Sci. 98 (2001) 8614.
[5] T. Shibata and A. S. Mikhailov, in preparation.