 The phosphorylation can furthermore be catalyzed by Cdc28-Cln.The inactivated CDC6 is then targeted for degradation by SCFCDC4-dependent ubiquitinylation and afterwards degraded by the proteasome.Thus, the regulation of CDC6 is tightly correlated to the activity of Cdk2 and since Cdk2-activity is oscillating once per cell cycle, the accumulation and degradation of CDC6 also oscillates.