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To characterize the human elk-1 promoter , we mapped the transcriptional start site and isolated elk-1 -specific genomic phage clones that contained extensive upstream and downstream sequences .
 human elk-1 promoter, elk-1 -specific genomic phage clones, elk-1, elk-1, transcriptional start site
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:
 human elk-1 promoter, elk-1 -specific genomic phage clones, elk-1, elk-1, transcriptional start site