4683
This polymorphism at residue 57 is a recurrent feature of HLA-DQ evolution , occurring in multiple distinct allelic families , which implies a functional selection for maintaining variation at this position in the class II molecule .
 ( protein: class II molecule, None) 
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: RNA,cell type,protein,cell line,DNA, Arguments type: . 
Text: {0} 
Answer:
 ( protein: class II molecule, None) 