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We have employed the ZEBRA /EBV biological system to test whether a heterologous activation domain can substitute for another activation domain (the ZEBRA domain ).
 ZEBRA, heterologous activation domain, ZEBRA, ZEBRA domain
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 ZEBRA, heterologous activation domain, ZEBRA, ZEBRA domain