CDKN1B and neoplasm: Furthermore, tumor suppressor activity of p27 was found to be dependent on its gene dosage.80 This role was further supported by investigating the phenotype of mice lacking Skp2, a component of an ubiquitin ligase that is part of the ubiquitin-proteasome pathway, which controls the fluctuations of p27 levels.82 Besides displaying a decrease in body weight due to increased p27 levels, these mice exhibit abnormal numbers of centrosomes; this phenomenon may be attributed to the presence of p27, as in Skp2−/−/p27−/− mice centrosome abnormalities were much less pronounced.83, 84