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Furthermore , by establishing the kinetics of usher - catalysed reactions between various pilus subunits , we establish a complete kinetic model of tip fibrillum assembly , able to account for the order of subunits in native type 1 pili .
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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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