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The structural genes encoding glyceraldehyde - 3 - phosphate dehydrogenase ( GAPDH ) , 3 - phosphoglycerate kinase ( PGK ) and the N - terminal part of triosephosphate isomerase ( TIM ) from mesophilic Bacillus megaterium DSM319 have been cloned as a gene cluster ( gap operon ) by complementation of an Escherichia coli gap amber mutant .
 glyceraldehyde - 3 - phosphate dehydrogenase, GAPDH, 3 - phosphoglycerate kinase, PGK, triosephosphate isomerase, TIM, gap operon, gap amber mutant
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 glyceraldehyde - 3 - phosphate dehydrogenase, GAPDH, 3 - phosphoglycerate kinase, PGK, triosephosphate isomerase, TIM, gap operon, gap amber mutant