In this task, you are given a sentence. You are expected to recognize the name of gene or protein. Although there might be several correct answers, you need to write one of them.
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Question:  Indeed , after a single oral dose , the role of the mu - receptor agonist component of the antinociceptive effect of tramadol appears to be minor , with most of the analgesic effect being attributable to nonopioid properties of the parent compound .

Answer: mu - receptor


Question:  Three experiments using 20 microM 2 - ( hydroxyamino ) - 1 - methyl - 6 - phenylimidazo [ 4 , 5 - b ] pyridine ( N - OH - PhIP ) were performed to induce mutations in the dihydrofolate reductase ( DHFR ) gene of a hemizygous Chinese hamster ovary ( CHO ) cell line ( UA21 ) .

Answer: dihydrofolate reductase


Question:  The predicted amino - acid sequence includes an N - terminal signal sequence of 27 amino acids , a 27 amino - acid pro - region , a 251 amino - acid catalytic domain typical of a serine protease with trypsin - like specificity , and a C - terminal hydrophobic extension which is predicted to function as a membrane anchor .

Answer:
serine protease