7397
Comparison of the proportion of nonsynonymous ( pN ) and synonymous ( pS ) substitutions occurring per site within tamarin variable region genes demonstrated a reduction in pN in the framework regions compared with pN in the presumed MHC contact regions ( CDR1 and CDR2 ) .
 tamarin variable region genes, MHC contact regions, CDR1, CDR2
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 tamarin variable region genes, MHC contact regions, CDR1, CDR2