22011
We purified the intermediate prohead II form , which is competent for packaging the 121 - kbp dsDNA genome , and we investigated its morphology and dimensions using cryo - electron microscopy and small - angle X - ray scattering .
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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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