Individual yeast cells signal at different levels but each with good precision

Signaling noise created by different kinds of biochemical stochasticity obscures information that cells transmit from surface to nucleus. Because different isogenic cells exhibit widely different responses to the same extracellular signal, a number of recent publications assert that this noise is large enough that single cells cannot make reliable decisions. Here, we analyze previous data on gene expression induced by the Saccharomyces cerevisiae pheromone response system. Individual cells signal consistently over time, implying that variability arises primarily from stable cell-to-cell differences, instead of noise. Our work shows that individual cells transmit, at a minimum, 2.7 bits of information through the pheromone system, and so each cell can distinguish at least 6 pheromone concentrations. Internally referencing responses with measurements of constitutively expressed genes improved precision to 2.9 bits. Combination with prior results showed that only about 6% of total response variation arose from signaling pathway noise.