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Answer:
Option a. met3, Met3p, MET3 is correct answer
"An investigator is studying mutants in methionine synthesis. The _met3_ mutants are unable to ATP sulfurylase, also known as _Met3p_. This protein is the product of the _MET3_gene. "
Explanation:
MET3 encodes ATP sulfurylase, which is a catalyst of first step of the sulfur assimilation pathway. This pathway results in the formation of hydrogen sulfide which is a precursor in the biosynthesis of cysteine, homocysteine, and methionine.
Source: National Center for Biotechnology Information, U.S. National Library of Medicine