20891
By tethering either DNA or PcrA to a microscope coverslip surface , unwinding of both linear and natural circular plasmid DNA by PcrA / RepD was followed in real - time using total internal reflection fluorescence microscopy .
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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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