548
These studies identify p21ras as a target of NO in T cells and suggest that NO activates p21ras by an action which mimics that of guanine nucleotide exchange factors .
 ( cell type: T cells, None) , ( protein: p21ras, None) , ( protein: guanine nucleotide exchange factors, None) , ( protein: p21ras, 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 type: T cells, None) , ( protein: p21ras, None) , ( protein: guanine nucleotide exchange factors, None) , ( protein: p21ras, None) 