Rate-limiting factors for G1/S transit.

<p>(A) Plot depicting the evolution of the rate of G1-phase progression () as a function of and for a simultaneous step of and signals. (B) Time-dependent changes in normalized concentration of the main G1 regulatory components following cell exposure to a simultaneous step of and signals at time . Before that time, and the cell stands in a G0-like state. Entry into S phase is assessed by the sharp rise of E2F at time . G1-phase duration is defined as the time gap . Four combinations of signal intensities are considered: (a) , ; (b) , ; (c) , ; (d) , . According to the terminology in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035291#pone-0035291-t001" target="_blank">Table 1</a>, the concentrations shown are: (dashed line), (dotted line), (dash-dotted line), (full line).