Spectral unmixing reveals the timing of expression of the GAL genes. Cells were grown in 2% raffinose, transferred into galactose and followed in the plate reader. a) Left-hand axis: Time-series data for mean fluorescence per cell for the Leloir enzymes Gal1, Gal7, and Gal10 and for the galactose permease, Gal2, and the regulators Gal3 (an intracellular sensor of galactose) and Gal80 (a repressor of GAL expression) in 1% galactose. Right-hand axis: Relative cell density (orange). b) The same data in a, but with the time-series of expression for each gene normalized by its maximum value. The normalized level of expression is indicated by the colour bar. c) A similar plot to b but for GAL expression in 0.1% galactose. Derivation of the error bars shown is given in Methods.