Precision of adaptation in wild-type cells.

<p>(<b>A</b>) Example FRET measurement of the pathway response. Cells expressing the CheY-YFP/CheZ-CFP FRET pair, a reporter for kinase activity, were stimulated by step-like addition (down arrow) and subsequent removal (up arrow) of 30 µM MeAsp, a nearly saturating stimulus. Changes in kinase activity in response to addition of attractant were used to determine adaptation time (<i>t_1/2</i>), defined as the time required to regain 50% of the initial loss in activity, and imprecision of adaptation (<i>i</i>), defined as the difference in the YFP/CFP ratio between cells adapted to buffer (interpolated grey solid line) and to a given attractant concentration (parallel dotted line below). Precision of adaptation (<i>p</i>), the fraction of kinase activity recovered in the presence of ambient ligand, was then obtained as 1−<i>i</i>, with 1 being the maximum possible precision (see <i>Materials and Methods</i> for details). The upward drift of the baseline is due to faster photobleaching of CFP compared to YFP. (<b>B</b>) Dependence of precision of adaptation on attractant concentration in wild-type strain SN1 [LJ110 Δ(<i>cheY cheZ</i>)]. Values were normalized to the response of buffer-adapted cells to a saturating ligand concentration. Some data in (B) were replotted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084904#pone.0084904-Neumann1" target="_blank">[14]</a>. Error bars here and throughout indicate standard errors for multiple measurements. (<b>C</b>) Dependence of precision of adaptation on adaptation time. (<b>D</b>) Comparison of precision of adaptation for MeAsp (orange symbols) and serine (blue symbols) in strains SN1 (closed circles) and VS104 [RP437 Δ(<i>cheY cheZ</i>), open circles] with dose-response curves of <i>cheB</i> strain VS124 [RP437 Δ(<i>cheB cheY cheZ</i>)] for steps of MeAsp or serine (open diamonds). Relative kinase activity was calculated as described previously <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084904#pone.0084904-Sourjik2" target="_blank">[16]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084904#pone.0084904-Sourjik3" target="_blank">[17]</a> and fitted by a multisite Hill equation <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084904#pone.0084904-Sourjik3" target="_blank">[17]</a>.