| Here we report that acute depletion of ORC 2 by RNA interference ( RNAi ) arrests cells with low cyclin E CDK 2 activity . ^^^ This result suggests that loss of a replication initiation protein prevents progression of the CDK cycle in G 1 . p 27 and p 21 proteins accumulate following ORC 2 RNAi and are required for the CDK 2 inhibition . ^^^ Therefore , the CDK 2 inhibition observed following ORC 2 RNAi seems to protect cells from premature S phase entry and crisis in DNA replication . ^^^ These results demonstrate an unexpected role of ORC 2 in CDK 2 activation , a linkage that could be important for maintaining genomic stability . . ^^^ |