6635
Gel mobility shift assays indicated that at least four nuclear proteins with distinct biochemical and binding properties possess the ability to bind the 3 beta I - A element to produce four DNA - protein complexes ( R1 to R4 ) .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 None