FIG. 4.

Pol I activity is not elevated in fibroblasts from p130^−/− p107^−/− double knockout mice. (A) Northern blot analysis of total RNA (10 μg) from wild-type (wt; lanes 1 and 3) or p130^−/− p107^−/− double knockout (lanes 2 and 4) fibroblasts that were actively growing in 20% serum (lanes 3 and 4) or made quiescent by culture for 24 h in 0.5% serum (lanes 1 and 2). The upper panel shows the blot probed with an 18S rRNA gene fragment, and the panels underneath show the same blot that has been stripped and reprobed with ARPP P0 and α-tubulin gene fragments. (B) The 18S rRNA signals were normalized against the ARPP P0 signals, as determined by PhosphorImager, and the mean values from three independent experiments are represented graphically underneath. Data obtained in the same way for 28S rRNA are also presented.