9552
The effect of the pRB posttranslational modification during apoptosis was investigated by determining the E2F-1 levels and by isolating and characterizing pRB -null clones from U937 cells .
 ( cell line: pRB -null clones, None) , ( protein: pRB, None) , ( cell line: U937 cells, None) , ( protein: pRB, None) , ( protein: E2F-1, 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:
 ( cell line: pRB -null clones, None) , ( protein: pRB, None) , ( cell line: U937 cells, None) , ( protein: pRB, None) , ( protein: E2F-1, None) 