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The failure to express a class II gene in at least one such mutant line has been mapped to the MHC class II X box , a conserved transcriptional element in the promoter region .
 DNA: promoter region; DNA: class II gene; DNA: MHC class II X box; DNA: conserved transcriptional element; cell line: mutant line
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 DNA: promoter region; DNA: class II gene; DNA: MHC class II X box; DNA: conserved transcriptional element; cell line: mutant line