<p>(<b>A</b>–<b>D</b>) BJ hTERT cells were plated and shifted to various first blocking conditions for 48 hr as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074157#pone-0074157-g001" target="_blank">Figure 1A</a>. The cells were subsequently shifted to CM or different second block conditions containing [<sup>3</sup>H]-TdR for 24 hr, after which the cells were collected and the incorporated label was determined. Error bars represent the standard error for the experiment repeated at least four times. (<b>E</b>) Schematic model showing relative positions of different metabolic checkpoints relative to R (not drawn to represent precise time scales). G1-pm is post-mitotic phase in G1, G1-ps is pre-S phase of G1 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074157#B4" target="_blank">4</a>].</p
