5674
The R2 region within the class I enhancer acts as a negative element in Ad12 - transformed cells and exhibits a stronger binding activity than is observed in nontumorigenic Ad5 - transformed cells , which are not reduced in class I expression .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 None