Detection of p19-CDK complexes in vivo. Lysates of parental 32D cells transfected with the naked vector (lanes 2 and 3) or of clone 2C cells (lanes 4 and 5) either untreated or treated for 5 hours with 75 μmol/L zinc (as indicated above the lanes) were immunoprecipitated with antisera to p19 or to cyclin D3 (designated by IP, right margin) and then blotted with antibodies to p19, cyclin D3, or CDK4 (as indicated by Blot, right margin). Lysates from control cells were precipitated with nonimmune serum (NRS, lanes 1). Recombinant proteins produced in Sf9 cells were loaded as positive controls (lane 6) for the immunoblots.