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.

Q:  To further identify the residues responsible for the activity , we isolated the mutant viruses that were not neutralized with the soluble form of MHV receptor proteins , since such mutants were expected to have mutations in amino acids responsible for receptor - binding activity .

A: MHV receptor proteins
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Q:  Pancreatic expression of the glucagon gene depends on multiple transcription factors interacting with at least three DNA control elements : G1 , the upstream promoter element , and G2 and G3 , two enhancer - like sequences .

A: glucagon gene
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Q:  This is consistent with the need for a nuclear retinoid receptor function in RA - induced ERK2 activation .

A:
retinoid receptor
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