45
The result is two - fold : the His - tag facilitates purification by immobilised metal affinity chromatography , whilst the fusion domains act primarily as solubility aids during expression , in addition to providing an optional purification step .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Anatomy 
Text: {0} 
 Entities:  
Answer:
 None