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Alteration of LIN28 protein levels also negatively regulated the abundance of some but not all let - 7 miRNA family members , indicating sequence - specific binding of let - 7 precursors to LIN28 proteins and competition with cytoplasmic miRNA biogenesis factors .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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