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We have systematically analyzed the functional roles of these factor binding motifs of HS-40 by site-directed mutagenesis and transient expression assay in erythroid cell cultures .
 ( cell line: erythroid cell cultures, None) , ( DNA: factor binding motifs, None) , ( DNA: HS-40, 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: erythroid cell cultures, None) , ( DNA: factor binding motifs, None) , ( DNA: HS-40, None) 