721
When transfected into K562 cells , which express zeta-globin , comparable amounts of activity were obtained from the -557 and -417 zeta- luciferase constructs and the alpha- luciferase constructs when no enhancers or the alpha-globin locus enhancers were used.
 luciferase, enhancers, alpha-globin locus enhancers, alpha- luciferase constructs, K562 cells, -557 and -417 zeta- luciferase constructs, enhancers, luciferase, zeta-globin
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:
 luciferase, enhancers, alpha-globin locus enhancers, alpha- luciferase constructs, K562 cells, -557 and -417 zeta- luciferase constructs, enhancers, luciferase, zeta-globin