13663
Initiation of proliferation but not of differentiation was followed by a 20- to 25-fold increase in the nuclear level of the DNA polymerase-associated processivity factor PCNA and of the proliferation-specific transcription factor E2F1 .
 ( protein: DNA polymerase-associated processivity factor PCNA, None) , ( protein: E2F1, None) , ( protein: proliferation-specific transcription factor E2F1, None) , ( protein: PCNA, None) 
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: RNA,cell type,protein,cell line,DNA, Arguments type: . 
Text: {0} 
Answer:
 ( protein: DNA polymerase-associated processivity factor PCNA, None) , ( protein: E2F1, None) , ( protein: proliferation-specific transcription factor E2F1, None) , ( protein: PCNA, None) 