4067
Gel-retardation experiments show that Spi-B can bind to all putative PU.1 binding sites , but do not reveal any preferred Spi-B binding site .
 ( protein: PU.1, None) , ( DNA: Spi-B binding site, None) , ( DNA: putative PU.1 binding sites, None) , ( protein: Spi-B, None) , ( protein: Spi-B, 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: PU.1, None) , ( DNA: Spi-B binding site, None) , ( DNA: putative PU.1 binding sites, None) , ( protein: Spi-B, None) , ( protein: Spi-B, None) 