Fig. 3. (A) Analysis of p25-Cdk5 complex. Cell lysates from NGF-p25 and NGF-mock cells (used as negative control), treated for 6 hours with tetracycline, were subjected to immunoprecipitation (IP) by antibodies against either the p35 C-terminus or Cdk5. Immune complexes were then analysed by western blotting (WB) with antibodies against the p35 C-terminus and Cdk5. (B) Analysis of roscovitine's effect on earlier Rb phosphorylation. NGF-differentiated p25 cells were induced (+) or not (–) with tetracycline for 6 hours in the absence or the presence of 5 µM roscovitine (–/+). Lysates were immunoblotted with antibody against phospho-Ser807/811 Rb (P-Rb) followed, after stripping, with the phosphorylation-independent antibody (IF-8) against Rb protein (Rb).