6113
When expressed alone in test cells , Atr - I is unable to bind TGF - beta , activin , or bone morphogenetic protein 2 .
 Atr - I, TGF - beta, activin, bone morphogenetic protein 2
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 Atr - I, TGF - beta, activin, bone morphogenetic protein 2