1655
Expression , nucleotide sequence and mutational analysis of two open reading frames in the nif gene region of Anabaena sp . strain PCC7120 .
 nif gene region of Anabaena sp . strain PCC7120
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 nif gene region of Anabaena sp . strain PCC7120