NEWS AND VIEWS A noisy ‘Start ’ to the cell cycle

In small cells like a bacterium (volume B1 fl) or a budding yeast (volume B100 fl), critical intracellular regulators are often present in small absolute numbers. In Saccharomyces cerevisiae, it is not unusual to find mRNAs expressed at concentrations of less than one molecule per cell (Ghaemma-ghami et al, 2003). This means that cells will sometimes possess no molecules of some particular mRNA, sometimes one molecule, and sometimes two or more. How can cells function properly in the face of such dramatic stochastic variation? Experimental studies of the noise in synthetic gene expression networks have begun to provide important insights into this question (Elowitz et al, 2002; Raser and O’Shea, 2004; Pedraza and van Oudenaarden, 2005). Recently, Bean et al (2006) have taken an important next step in the analysis of noise, by applying modern single-cell fluorescence reporte