5246
Binding of SSP to the stage selector element ( SSE ) in the proximal gamma - globin promoter is integral to the competitive silencing of a linked beta - promoter in embryonic / fetal stage erythroleukemia ( K562 ) cells .
 SSP, stage selector element, SSE, gamma - globin promoter, beta - promoter
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 SSP, stage selector element, SSE, gamma - globin promoter, beta - promoter