4213
The tro operon is flanked by a Holliday structure DNA helicase homolog ( upstream ) and two ORFs representing a purine nucleoside phosphorylase homolog and tpp15 , a previously characterized gene encoding a membrane lipoprotein ( downstream ) .
 GENE: tro operon; GENE: Holliday structure DNA helicase; GENE: purine nucleoside phosphorylase; GENE: tpp15
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: GENE 
Text: {0} 
Answer:
 GENE: tro operon; GENE: Holliday structure DNA helicase; GENE: purine nucleoside phosphorylase; GENE: tpp15