S1Supplemental Data Subcellular Localization Determines MAP Kinase Signal Output

Supplemental Discussion Thus, K can be determined by the activity of Raf, which gives half of the maximal percentage of the activated cells. With the given experimental measures (xi, yi), i 1,K,N, where xiIs the MAPK Module Really a Switch at the Plasma Membrane? is the activity of Raf and yi is the percentage of the activated cells, we tested different Hill coefficients and dissociation constants. Be-Cytoplasmic activation of the MAP kinase module is clearly switch like because throughout the transition range between zero and satu- cause no intermediate data points exist, we generated curves of best fit and chose the Hill coefficient when the difference betweenrating activity, single cells distribute between one of two discrete activation states, “on ” or “off. ” The membrane system, because of the experimental results and the estimated Hill coefficient equation was minimal, namely:its increased sensitivity to input, is maximally activated even at the lowest level of input, and all cells are in the “on ” state: in our hands, the membrane system was maximally activated with as little as E N i1 |yi h(xi) | min. (2)3 % increase in Raf input (see Figure S2). There are two possible interpretations of this data: (1) the membrane system is switch like