5492
A genetic system was devised to select for pi protein mutants which discriminate between IR and DR ( York et al . , Gene ( Amst . ) 116 , 7 - 12 , 1992 ; York and Filutowicz , J .
 pi protein mutants
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 pi protein mutants