Immuoblots and BrdU immunofluorescence assays were carried out as described previously [13 (link),14 (link)]. The following antibodies (all from Santa Cruz Biotechnology) were used: anti-p21 antibody (clones M-19, C-19 and F-5), anti-TRIM3 antibody (clone 27), anti-c-Myc antibody (clone 9E10), anti-HA (haemagglutinin) antibody (clone Y-11), anti-tubulin antibody, anti-GST antibody (clone B-14), anti-BSA antibody (clone A23-A/D3) and anti-p27 antibody (clone C-19).