Signaling pathways relay information about changes in the external environment so that cells can respond appropriately. How
much information a pathway can carry depends on its bandwidth.
We designed a microfluidic device to reliably change the environment of single cells over a range of frequencies. Using this device,
we measured the bandwidth of the Saccharomyces cerevisiae
signaling pathway that responds to high osmolarity. This prototypical pathway, the HOG pathway, is shown to act as a low-pass
filter, integrating the signal when it changes rapidly and following
it faithfully when it changes more slowly. We study the dependence of the pathway’s bandwidth on its architecture. We measure
previously unknown bounds on all of the in vivo reaction rates
acting in this pathway. We find that the two-component Ssk1
branch of this pathway is capable of fast signal integration,
whereas the kinase Ste11 branch is not. Our experimental techniques can be applied to other signaling pathways, allowing the
measurement of their in vivo kinetics and the quantification of
their information capacity.